I am going to take a stab at this, however, I still think, as many others, that you are asking for too much. You also mentioned legal, which many times, is taken as a threat and sent to the legal department where, in this case, probably was thrown away. Unless the laws are different where you come from, you would most likely not prevail in a lawsuit for half of your stay.
Also, it was not made clear that you had been through the suggested process in your original post, just that you had written. Had you actually followed the guidelines of the letter writing, your last bullet point would and should have been left off. This is the fastest way to not hear back from anyone.
We had an entirely unsatisfactory stay due to: Had your stay been that unsatisfactory, then you really should have left and mitigated your damages. Was each and every day of your stay absolutely miserable? Did you enjoy absolutely nothing? A better start would have been, "We had a less than stellar stay due to: (you have now left room for some good)
* Being promised a quiet room, yet there are no quiet areas within the resort. We had constant disturbance from staff in corridors, and in rooms next door. What were the exact noise complaints? Quiet is subjective. A hotel is never going to be 100% quiet, there will always be some level of noise, be it from water running in the pipes between floors, people going in and out of rooms, the dings of elevators. What were the constant disturbances? To me, this is too vague to do anything about and does make it seem like you have unrealistic expectations of any hotel. A better sentence/ complaint would have been: Being promised a quiet room, yet, our neighbors slammed their door from midnight until 6 am and after calling the front desk, the situation did not get better. Additionally, the people staying above us sounded like they let their kids jump on beds. After repeated complaints to the front desk (or manager) none of this was addressed, nor were we provided an alternate location in the hotel. You should not lump staff into the complaint if they were carrying out their job duties, for instance cleaning the rooms next to yours, vacuuming the hallway, etc. Unless this happened between the generally accepted quiet hours of 10PM and 6AM.
* Due to the lack of provision for quiet areas in the resort, guests were noisy and disturbed us morning and night, even when in our room. See above
* The noise in the dining areas hit 90 decibels regularly, the same level as a rock music concert. And yet the resort promises 'laidback dining'. Did you ask for a quiet table? Did you attempt in your long stay to see if some areas of the dining room were more quiet than others? I am with you 100%, in that I hate loud dining places. I refuse to go to some because it annoys me so much. I am not really sure what the hotel could have done to alleviate this, as sometimes it is building acoustics. I guess you could have taken all the meals in your room. Did you have a reasonable solution you presented to the manager that was just ignored?
* Our daughter was exposed to Disney cartoons despite kids club staff being told she reacted badly to this. Was your daughter the only child in the kids club? If not, most kids clubs cannot and will not cater to just one kid. When I was a teen, I was a nanny for a summer and the parents had strict TV/video game time, but that is why they hired me instead of taking them to a day care. I know it seems like an easy request, but what about the 15 other parents who wanted their kids to watch Disney? Where do your rights begin and end versus others who are utilizing the same services?
* She also had an accident which was undocumented in the kids club despite the fact she injured her toe. How badly was the toe injured? I do think this should have been documented, if it was broken, but a scrape? The staff would spend all day documenting minor injuries. Should the parents be notified, yes. If it is major (again subjective), then yes document.
* Our daughter was never offered water and was dehydrated from being in the kids club. They fed her processed food (without our permission or knowledge) when she only ever eats fresh, healthy food. This is a legitimate concern. Did you speak to the management, was anything offered? Did you notify the hotel and follow up with the kids club of her special dietary needs? Again, this is not private babysitting, this is akin to a day care, where they are catering to many, not just to one. If you had gone over special dietary needs before hand, then you have a complaint. Also, once this happened, did you pull your child from the kids club so that you could monitor her hydration and food needs? Because if I had a kid with special dietary needs and the day care did something wrong and did not address it appropriately, my child would not be going back.
* Food in the buffet was unsafe to eat and was regularly cold. Hairs were found in the food. At every meal? Did you alert the staff and management each time? Did you get sick?
* Tours were regularly quoted at different prices even within the hotel by different staff who were clearly trying to make extra personal income. I think this is legitimate to complain about up to a point. This may be similar to a cruise line selling an excursion for $100 when had you just gone to the provider, cost would have been $80. A convenience fee, so to speak. Again, was this brought up immediately with the manager? How do you know the staff may not have been quite sure of the price, so overstated it. What if the staff had understated the price, and then when you got to the tour, all the sudden it was more?
* The drains were regularly blocked in the resort and in our room the toilet leaked effluence onto the bathroom floor. This is also a legitimate complaint. When you complained, were you offered any sort of compensation? If not, did you ask then and there? How often did this happen? Was it daily? Did you ask to move rooms? Was the problem fixed within a reasonable amount of time?
* We raised our concerns with Winsome Hooper and Clark Lobban the guest services and hotel manager. They were exceptionally rude and dismissive and told us we could leave if we didn't like it and did nothing to help us or fulfill the hospitality promise. I know I kept asking above, and you stated this here, but did they literally not address any of your complaints? At what point did they basically say to either quit bothering us or leave?
* We were never able to 'Stay Impressed' as per the Holiday Inn slogan. I would move this to the first of the complaint and remove the word never. Something along the lines of, Your Holiday Inn slogan is for guests to stay impressed and we were unimpressed with our stay...
* The resort was unpleasant to stay in and felt dangerous. Rational people do not stay in an unsafe resort with their child. Not ever. Leave this out. Had you truly felt unsafe, you would have moved to the 5x more expensive hotel in a heartbeat and amended your vacation plans.
* We have photographic and audio evidence of the worst aspects of our stay and are well aware of the legal compensation available in such a situation. This right here is almost 100% why your complaint is being ignored. You mentioned legal compensation. The hotel is now awaiting your lawsuit. Legal has been given your e-mails and has probably started a file. But most employees have been told to no longer correspond with you due to your threat of legal action.
You can try writing again, utilizing everything that has been pointed out in the comments. I am not sure it will do any good at this point, but may be worth a try. I think 1-2 nights off of your stay is appropriate until more details are given. I think 50% off is unreasonable due to the facts I have right now.