The Diplomat should be like the Warlord so the user pays the build cost to take a building. However, instead of the building being destoyed, it arrives in the Diplomat city. The buildings that are 6/8 then become targets as well as as the Dark City building worth extra points due to cards under it. For these buildings, the Diplomat gets extra victory point value while also depriving the owner of the building. A suggested alternative is to make the exchange cost of the building the VP value not the building cost. In either case, the Diplomat should target purple buildings!
Diplomat character unfair?
I think the Diplomat as printed works just fine, although your modification is certainly interesting.
Building cost and VP are the same on, what, over 90% of the buildings? If you're worried the diplomat will take your dragon's den then don't play it till the end.
Heh. Half of the star cards are unfair...thats what makes them interesting to mix in.