I've watched dozens of lectures from Jacob Appelbaum and Roger Dingledine via Youtube.. I've taken the time to watch 3-hour Q&A sessions with them, I've read interviews with them.
And aside from brief, "Hey, folks, hidden services need some love" style short comments, I've never heard them spend much time or energy on hidden services.
It's not part of their message. I believe that's intentional on their part. And I think that their aversion to bitcoin goes along with their efforts to stay focused on keeping the conversation on technology and Iranian dissidents. By not devoting any actual Tor Project developers to hidden services, and not accepting bitcoin (and a bitcoin-funded grant for hidden services would follow shortly after they started accepting them, I'm sure), I think they try to straddle the fence. Lecture about The Four Horsemen (drugs, CP, money laundering, terrorism) being distractions, and free speech being their focus.
I totally agree with the OP's core point, but I'm guessing it's harder than it looks. Bitcoin isn't the same as cash, and non-profits accepting money from Uncle Sam have a million reporting/audit requirements that I'd rather die than understand. They have to balance their funding needs, and while Uncle Sam's funding may shrink in the future, it won't shrink as much as DPR's would have in early September.
The other issue is finding the right person to actually improve hidden services.. there are a finite number of individuals who really *get* the complexity of the issues involved. But if someone who was flush with bitcoin and passionate about hidden services could find the right person, it's a no brainer.