About "this is an open-source, free project, so we have no control over people and can't force them to do what needs to be done" – this is simply not true. It is not a secret, that once a salary of a developer in a company reaches a certain minimum level, money stop to be the primary motivator. Non-tangible things become more important.
Since people come work here without pay this means they already have the basic level of income. They can be teenagers, living off their parents. They can be students. They can be people with day job or people with external income sources. So the money is not the primary motivator here (duh!).
Ok, how about fixing a few of our old and boring bugs? Got motivation to fix partitioning in the first stage setup, for example, by rewriting old code? Motivation? It gives more usability to the project.
Just an example.
WBR, Aleksey Bragin.