Re 'community,' I am not persuaded that larger all by itself means better, and I suspect it tends to be as much or more of a problem as a benefit.
A larger community means more custom made content, bugs reported earlier, game questions/problems answered more quickly, more spread of the game by word of mouth, etc., etc., .
Exactly what problems exist from a larger forum community as compared with a smaller forum community? I can't think of any problems which would be so extreme as it would tip the scales against all the benefits.
Longer-lived is good, but one reason the boards at GC2 can look 'dead' to casual visitors is that the cross-forum sprawl has discouraged a lot of former regulars who find it tedious to dig through all the general PC talk, Off-Topic rants and silliness, and Impulse shakedown chatter.
Dominions_3 also have lots of general PC talk, Off-Topic rants and silliness on their forums. One of the most active forum sections on Dominions_3 is the multiplayer section.
GC2 was released over three years ago, and we have a brand new Metaverse empire, not quite a month old, with their own non-Stardock site.
Gal_Civ_2 was released in Feb_2006 and Dominions_3 was released in Sept_2006... yet Gal_Civ_2 had the benefit of multiple paid internet advertisements and having multiple expansions officially released in stores. The last expansion for Gal_Civ_2 was released only a year ago. The new GC2 Metaverse forums are just as deadly quiet.