I'll go ahead and compile my comments into a real answer so that people can up- or downvote it.
It's true that answered id requests are basically worthless. This is one of the many reasons I don't think having id requests adds much to the site. For example, we had seven id requests looking for Shinzo—that's one two three four five six seven. Clearly the previously answered questions weren't helping anyone.
However, I don't think this proposal is an answer to that problem. The details the OPs remembered on each of those seven questions are different enough that the OP probably never would have realized the other six questions were looking for the same show.
I also don't think this proposal will be particularly helpful to people answering id requests. Google is an amazingly powerful tool for searching information, and not just information on our site. Chances are, if you can find the answer by browsing a giant list of previously answered id requests, you can find it more easily using Google. And if you do think that looking at previously answered id requests will help you, we have a search bar, which I used to find those seven questions looking for Shinzo. (I originally thought it was five, but the search turned up a couple I hadn't known about.) You can also use Google for that: do a search with site:http://anime.stackexchange.com. For instance, I found the Shinzo identification requests again by doing a search for shinzo "identification request" site:http://anime.stackexchange.com on Google.
I think the gains here will be marginal. If it were a small amount of work, it might still be worth doing, but it won't be a small amount of work; it will be gargantuan. We have over 2,000 identification request questions, with about 280 of them unanswered. So members of the site will have to go through the remaining ~1720 id requests, see what the answer turned out to be, then go to another page with an index of anime and manga, find the one which answered the id request, and edit the entry to add a link to the question. That's for the ones which actually have accepted answers; a bunch of them have answers which aren't accepted, because the OP ran off. A bunch also have answers in comment threads. So you have to read every piece of text on the page to make sure there isn't an answer buried in some comment thread underneath a wrong answer. And then we need people to keep doing this for every single new id request that gets answered.
We don't actually have that many people on this site doing maintenance and review tasks. During the image-only id request cleanup, I kept seeing the same eleven or twelve names on all the close votes. So there's a shortage of workers even potentially willing to take on this gargantuan task.
Of course, if you just really really want to do this, regardless of the community's opinion, there's nothing stopping you. You can even do it offsite somewhere, like on GitHub or a blog, where you control the whole process. However, I would ask you not to promote Anime and Manga.SE as a site for identification requests; we already get plenty.
(Digression: recently, I've been trying to find an alternative site where we can direct id requests, and I think I've stumbled on the reason why we get so many: because none of the other obvious sites (Reddit, Quora, Yahoo Answers, MyAnimeList, etc.) seem to do id requests. The ones I did see on those sites had been either completely ignored or sloppily answered with something that was obviously wrong. By contrast, a certain contingent of users here leap to answer id requests, and will levy the full force of their usually considerable research skills to find the answer. Thus, our legend spreads throughout the Internet as a magical site that can find "Evangelion" given the description "I watched it when I was young, there was this nerdy guy in a white shirt and this girl with red hair and in one episode they went to a hot spring".)
I'll end this answer with some personal advice, which you are free to take or ignore. It might sound harsh, but it's meant to be helpful, so read it in that spirit.
You seem to be extremely excited about participating on Anime and Manga. That's good! We need people who are excited to participate. At the same time, I've noticed you doing some things, especially in the review process, that aren't productive or go against the policies of SE in general or Anime and Manga in particular. One of these came up in Is there a meta post here on Anime.SE that explains user bans?. I think you're getting too excited and rushing ahead to do things without finding out beforehand whether your actions are welcome or useful.
I recommend that you instead take your time getting acclimated to the site. Ask and answer questions instead of worrying too much about reviewing or side projects. Read the best questions and answers the site has to offer, and learn from them what a good question and a good answer look like. I think we have some of the most amazing posts on the entire SE network, and I learned a lot about what a good post looks like from reading them. Go to chat, if you want, and get other people's opinions. Doing this will also let you identify real problems that the community has, and come up with solutions that benefit everyone. SE is a community effort. Everyone builds and maintains the site together, and each site has a different culture. To make valuable contributions, you should make an effort to understand that culture.
