There have been discussions and ideas surrounding decaying votes, along with weights of votes themselves. I've got mixed feelings about both.
It's important to look at the utility of reputation, the degree that the system trusts you, before you consider the extrinsic motivation that it provides. Believe it or not, having someone arrive to your site and actually type something meaningful is quite an achievement. Having someone type something that is both meaningful and technically sound, however simple, is close to magic. I didn't realize how much this was the case until I started looking at tests that we run to try and understand visitor behavior. My point is, don't under-value contributions from knowledge that isn't rare, those are still valuable contributions.
Someone that has a track record of arriving to the site and doing meaningful, technically correct things should be given additional privileges - you'd be silly to not give them more ways to participate. Despite the actual extrinsic motivation, which is having a number associated with you increase as you see more and more people agree with what you wrote - the underlying system of trust is particularly good at giving the more skilled more tasks.
The idea of decaying votes becomes interesting because it would help to ensure that the most relevant, up-to-date answers would (at least, in theory) continue to rise to the top on older questions. On theoretical sites, or sites where domain knowledge is apt to change yearly, this becomes interesting. Your answer that got 400 up votes would need to continue to receive up votes as it aged, or answers that were receiving a greater velocity of votes would overtake it - a lack of votes on your answer being an indication that it isn't as relevant as it once was, and older votes would start falling off.
That would also be the mother of all headaches to implement. It's just an interesting theory.
Weighted votes for clearly demonstrated rare knowledge would be extremely cool, but not exactly accurate - if someone got 10,000 reputation for answering 100 very easy questions, does this qualify them to be a 'better' voter when it comes to those stellar answers that often go without due appreciation because they're difficult to understand? I'd tend to think not. If we did this, we'd have to do a combination of age, tag, rep, views to votes, snake oil and a little hoodoo - and it would still be wildly inaccurate and prone to abuse.
These are theoretical problems that I love to think about, because I do believe that an algorithmic solution could be in the midst.
Your best bet, for now is to share links to spectacular answers, and use the bounty system. If you really do believe that your rep was a little too easily earned, give it to users that tend to leave obsessively composed answers.
But, don't make the mistake of under-valuing your contributions here. Did I mention how hard it can be to get people participating on a meta site too? ;)