I was just wondering whether my upvoted questions or answers on ELU meta affect my reputation. If they don't, would we be able to make this a feature?
Questions and answers on Meta do not earn you reputation. The only exception, network wide, is questions on Meta Stack Exchange, the network meta.
There is a reason for this.
Reputation relates to your knowledge of the site's subject matter. Meta is not related to that subject, so the reputation does not count. MSE is different because Meta is the area of expertise.
Additionally, with things like Feature Requests, downvoting is a way to show disagreement, and the last thing you want to do is propose a disliked question or answer and then be punished for voicing it by losing a lot of reputation... or to be punished for downvoting answer posts you don't like.
Users should feel free to voice their opinions on Meta without worrying about whether those opinions are popular.
As such, voting on Meta does not and should not affect your reputation.
Related on MSE:
More info on this help page.