I agree with bits and pieces of what everyone is saying, but I feel that you should definitely practice more (that's not to say you're stuff isn't good right now).
See, it's kind of a conundrum - once you've made a name for yourself, people recognize you and vote you up (or down, if you are recognized for your very bad content) and up and up, which of course gets even more people to notice your work. This includes the admins of the site, too, which is why you may notice a lot of really well-known animators getting front-paged often. This isn't because the staff is picking favorites; it's because their content is repeatedly very good and a lot of people follow them and love noticing their content on the front page and seeing the new stuff they have out (although the favorites system is helping new submissions be noticed, too). However, the site staff also love finding and front-paging new up and coming talent and people that show they they have remarkable amounts of talent. This can be more difficult though, because if you're already not well known, it's harder to be noticed in the first place (which is what you're experiencing).
So I would just keep making a lot of stuff and collaborating and finding ways to get yourself OUT THERE, right in peoples' faces (politely, of course. You don't want to be that guy). I would start following suit of some others who you've noticed have a large following. Maybe you should start off with shorter animations? You don't have to make Pokemon, Mario parodies, etc., but you can make short skits of your own. You said you made a 20 minute long animation that took you three years to complete? That's really cool, but there will be no one to watch it when you've completed it and spent all of that hard work and time on it. Not until you've garnered yourself a considerable fan base. The best way to do that would be by submitting shorter movies more often - your name will come up repeatedly and soon people will recognize you when they see who made this submission, that submission, etc. It's important to make stuff frequently, because people will notice you easier this way. If you only pop up once every year or two with a submission, people likely won't retain your name in their memory.
Plus, you won't be burning yourself out. It sounds like you're putting a lot of stock into these larger animations of yours, and subsequently getting horribly disappointed when it seems like all that work was for moot. How about you try to make one animation every two months? Look at the Nata competition - one reason it is so popular amongst flash animators is not because of the prizes themselves, but because of the exposure they receive and the amount of animations they produce in a short period of time (also good exposure). So I think the best thing you can do for yourself is to make decent quality, short animations, perhaps one every few months, which will not only help you hone your skills but also help people on this site notice you more over time. Good luck, man!