Group matters, too....especially if it is a very good or a very bad group.....but that doesn't factor into whether or not system matters. Rather, it is similar to saying that the quality of your vehicle and the quality of the surface you are driving on both matter. If one really sucks, the trip sucks. If one is really great, it helps, but it is better to have the best of both.
I agree RC, to a certain extent. I think though that it depends on how much the DM and/or players wanna modify the system they choose to use.
For instance with a car trip you can't pave your own road. With an RPG you can,analogously speaking. You can modify anything you want. You can pave or repave the road as you like.
Now the trick is, as others have said, do you wanna, and how much time and effort is that gonna require (out of the DM or GM, and/or the players)?
As a kid I didn't care how much time it consumed. I could work it as I liked. (You know the old saw, as a kid you'll trade time for money, cause you got plenty of time, as a man you'll trade money for time, cause you don't have nearly as much.) As an adult I don't wanna hav'ta reinvent the wheel, I got far more important things to do with my time. However sometimes in my spare time I rework things anyways, cause it is a fun distraction and for once I don't have to be doing anything serious or anything others really need to rely upon me for. Nothing is at stake, so it's just entertainment and relaxation. (Same reason I come here. Now I think gaming can be useful, very useful. As training. And even productive on occasion. But the big advantages with gaming, and even with training is, most of the time, nobody is gonna get hurt. So it's far from the most important use of your time, but it's also far from the most dangerous or taxing use of your time. And sometimes that's just plain good enough.)
But that being said, about limitations on my time, I personally still (iffin I had to make a choice) would choose comrades over games, and friends over systems. After all we can still always remake the system into anything we want, or even create our own (as you alluded to), so you can always modify a game. Within reasonable time constraints of course. You can't really approach the problem in the same way when it comes to other people.
Ideally though you'd want good folks and a good system. But if the system doesn't please me to every extent then I can always refinagle that. Without too much problem.
And there are of course games I wont play. But mainly cause I don't have time to, or because the subject matter (what the game is about) doesn't really interest me.
But I've never in my whole life, even going back to wargames and the earliest editions of D&D, ever played an unmodified, exactly as structured RAW game. I've never seen RAW in any system that I thought covered everything, or everything well. So I've always modified everything. Sometimes a little, sometimes a lot. Then again only once have I ever really played with
