So far, pretty much everything has turned out well. A couple of minor things/wishes for improvements (in Crusade):
1. As Rhonin said, Diplomatic Corps should be 1-per-Player.
2. The AntiMatter Power Plant should likewise be 1-per-Player, but it needs downrated a bit. Maybe +3 instead of +5 for adjacency bonuses and give a +1 to Raw Production.
3. Bring back the Thulium Data Archive, Durantium Refinery, and Promethium Reserve from the base game. Properly balanced, they're fun.
Preliminarily, I'd say 100 Cost, +1 Maintenance, +1 adjacency bonuses, +5% per level themselves, then +1 research (TDA), +1 All Production (DR), and +2 Wealth (PR), with a 3 resource cost for each (Thulium/Durantium/Prometheon for TDA/DR/PR). That makes them nice for the early game, but not really too useful later on.