Generally I have been advocating interface improvements over features additions. Things like AJAX tag editing are much more valuable than comment up/downvoting, that's my guideline.

I think as things have got more complicated, the interface is getting more difficult to organise all one one page, it's getting inconsistent across pages, people argue about whether thing X should be at the top of the page or the bottom, people use different pages as their "main" page (queue, comments, profile, whatever)

The solution to this is my.videosift.com where users can add and remove widgets that display the info they are interested in.

e.g. i might have these widgets configured like this:
queue latest 10
current queue of farhad2000
last 10 threads i have commented in that have since received more comments
british channel latest 3
ant's downvotes latest 3
links to my favourite 10 users ranked by my upvotes
dead videos tagged airplane or beatbox, latest 5
search results for "russia"

All these things are not really feature additions, they are just SQL queries, they are not ridiculously hard to code, but they would transform my sifting experience and encourage me to participate more. There's your sticky feature. This would kick so much more ass than sift money in a clunky interface.