Your thoughts remind me a bit of the thoughts I had last summer. I’m far more relaxed nowadays…
Isn’t that always the case? I’d even go as far and claim that our contributor/user rate is pretty high since people are usually really interested in diasporas development. And even using diaspora is kind of contributing, isn’t it? 
We do not have a dedicated roadmap and honestly, I don’t think we need one. Every active contributor has their own goals and imaginations and that’s super cool. Some people want to work on Federation stability, some people want really bad to have an account migration feature and others want to finally implement mentions in comments. And I think that’s cool. We all treat diaspora* as a nice side-project we work on in our freetime, and we want to work on the stuff we really love to work on. I don’t think there is a need for a project-wide roadmap.
Even if someone wants to join without their own ideas, there are 62 confirmed bugs unresolved on GitHub and 240 feature requests tracked on GitHub. There is a lot of stuff to do and it’s pretty obvious what is important to the people involved and what is not important.
Well. That’s a very interesting question. The obvious answer is: Yes, sure! However, that entirely depends on the type of contributor. Right now, I don’t think we have the resources (or, FWIW, the motivation) to mentor a lot of “this is my first time contributing to Open Source” kind of people. Don’t get me wrong, these people are super awesome, but they take a lot of time to introduce and I am simply not sure if we want to do that.
These are just my two cents, looking forward to other opinions. Good to see you back. 