I've been interested in Celestia for a while but never seem to see anyone talk about it. I can see how it wouldn't have a lot of staying power but it sounds like it'd definitely be worth checking out eventually.
I'll spring Terra Nova on my group at some point, too. Terra Mystica (and Gaia Project by extension) is another one I've always been very intrigued by, but I do wonder if the more accessible version actually suits our collection better.
Chilly McFreeze
https://i.imgur.com/UYamul2.gif