Eh...The species the klingons could use I feel are fine for the moment. Of course you may make the arguement for the oddball joining starfleet from the klingon pool of species, and vice versa.
I feel that the KDF should and ought to maintain its current species list, and should get access to new species...IF....they are not at war with them. For example...I have seen people attempt to create other aliens that look like cardassians. If we aren't at war with them, then down the road, they should be available to us.
As for the fed side...There is already enough eye candy to keep you occupied. Let us klingons have what little (if any at this point) unique facotrs we have left. You know what fed whining gets...more ships and content; what's next? Taking and adding klingon species and content to the fed side?
Klingon whining (as it has been called) has gotten us one frakking lousy carrier, and a somewhat fix to the clipping issues in the game.....
Race != nationality and allegiance - thinking otherwise leads to terrible things that I don't think need to be pointed out directly. There will be people who disagree with the government of their homeland, or are from a colony that ended up changing hands, or are simply immigrants. I would like the ability to make characters who reflect that - and the C-store is good for that because a cost keeps them from proliferating too much.
The unique 'eye candy' factors the Klingons have do nothing to improve the KDF gameplay. Selling them and earmarking the proceeds to shift development time over to the KDF just might. I'm not asking for cloaks or Klingon ships in Starfleet, never have, and never will*, though I have repeatedly suggested that there should be more KDF ship options including the ships of their satellite states. Individual people of a species (and their fashion choices**), on the other hand, are absolutely not logical to completely restrict to one side and I think it sends a somewhat non-Trek message to do so.
*I have, in fact, referred to Starfleet getting cloaks as 'fail'.
**For off-duty wear, I really don't think there should be any species limitation anyway.