I have to agree with Thorsten: attracting "tinkerers" (those who want go get involved in modifying/extending the simulator) is analogous to "fueling" the project, i.e. it's the main currency that counts, not unlike a commercial project which needs to make revenue and profits to pay its developers - FlightGear developers/contributors aren't paid, so they need be motivated and rewarded differently, e.g. by allowing them to work on their area/s of interest, and spending time doing things they enjoy - which is how the project is kinda "self-organizing", with people listening carefully to what other
contributors are interested in, and their track records - to identify overlapping areas and efforts, and see if/how these can be coordinated to end up with a greater RoR.
This may sound unpopular for people not interested in contributing, especially those whose primary argument usually is that they /might/ become contributors at some point - but usually, that's really a moot point.
Which is also why it pays off for us to focus on providing support to other contributors/developers, instead of just end users - simply because there's much better leverage then. For instance, back when Thorsten started out here, some of us ended up supporting him - considering his results (screen shots, released scripts etc) as our "reward" - let's assume, that a new contributor receives ~50 hrs of support from other contributors - the same time spent supporting others (primarily end-users) does rarely -if ever- have such a great RoR.
In general, that is how most FG related efforts are likely to work behind the scenes - ideally, by people networking with others to find the corresponding skills/expertise and convince them to help with a certain effort, even if just temporarily.
From my standpoint, a nicer UI would be "nice" to have (and is in fact being woked on), but my focus would never be to attract more end users, hoping to turn them into contributors - in fact, I'd argue quite the opposite: end-users claiming that they cannot get involved right now,
due to FlightGear's GUI, are demonstrating a lack of patience and willingness WRT FG internals - which would almost certainly apply just as well to a future scenario, where a new UI may be available - and in fact, given ~3 different/independent recent UI efforts, I don't see any reasons for people -genuineley interested in an improved UI- not to get involved.
Which is meant to say that there may be a certain barrier to entry depending on your area of interests - but that also serves as a "filter" to help others determine how strongly someone is motivated, and how willing/able someone is able to follow up on his requests.
Which kinda sums up, why I ended up spending roughly ~20 hours to set up Thorsten with a working build environment a few years ago, despite him not being interested in cvs/git or cmake stuff - I knew how to script this stuff, and it was also obvious that Thorsten would regularly share his results (not just screen shots, but actual code/features) with us. Also, he was working on stuff that nobody else was working on, but that everybody appreciated.
Meanwhile, Thorsten is doing of fancy, and unprecedented stuff, that even most of us long-timers would not have been able to do in the same time frame - so whenever Thorsten is posting an update/patch or even just screen shots, it's kinda a "pat on our shoulder" looking back, knowing that we belonged to those who were trying to make this a positive experience from the get-go, while also understanding that some/many recent interactions may no longer be as positive
While this may sound a bit pompous, especially to Thorsten -given that he did all the hard work- it goes to show that there's a certain thought process involved, and no matter what side you're on, it does help to understand how this works.
I think I once mentioned this elsewhere: you could look at the way this works by looking at business angels assigning their venture capital: in the case of FG, our "capital" is our spare time, in combination with our expertise and skills that we can share with others, i.e. to "bootstrap" them and get them going until they've reached a point of self-sufficiency - at which point, they'll hopefully also adopt such a "business angel" attitude and look at the community to share their own time and skills with other contributors.
However, knowing fully well that many such efforts get killed early on, it does make sense to "cast your net wide" - and unless someone already has a certain track record, you'll end up supporting a handful, or maybe even a dozen different efforts at the same time - ideally, in a fashion that is not specific to a single contributor being a hit/miss (e.g. using the wiki to document efforts/projects, instead of "people").
Which also sums up the reasons why it is easier for certain contributors to bootstrap new projects, because they already have a track record and reputation/long-evity, while others are difficult to judge.