A way to discuss ideas for the site, vote on them, and incentivize the generation of good ideas. I sense that having this would be huge. a) I sense that there are a lot of good ideas out there in people's heads but that they haven't shared. b) I sense that by discussing things, there could be a lot of refinement of current ideas, and a lot of generation of new ideas.

By ideas for the site, do you mean changes for the site code? And if you mean changes to the code, do you mean the change ideas, or the change implementations?

The backend is open source, and posts were made in 2011 and 2012 on how to make modifications to the code so that users could submit improvements. I don't pay close attention, but my impression is that very few, if any, improvements have been submitted by users.

Issues can be reported (i.e. requests made) at the Google Code page. But resources to implement those changes are minimal, as I understand it.

It seems to me that the primary piece missing is the effort. Either volunteers need to familiarize themselves with the codebase and then make changes, or volunteers need to put up enough cash to hire devs to make changes. (Presumably the folks at Trike Apps, who would need to approve those changes anyway.)

A way for people to assign monetary value to requests ("I would pay $20 for five separate subreddits") and aggregate those pledges into prizes would perhaps be interesting and solve some of the core problems (while causing other, hopefully more minor, problems). Either it's clear that something is worth doing, it gets done, and the doer is rewarded, or it's clear that something is not worth doing, and it remains deliberately undone.