I don't care for the rolling of the die so many times which is one reason I prefer this over Risk.
I know what you mean. Rolling every time you conquer a region might be too much. I do want it to be random to some degree though. How about:
Mineral - At the end of your turn, roll the die. You receive as many mineral tokens as you roll and place them in your regions (no more than one per square). At the start of your next turn remove them from the board and receive one point per mineral token you take. If another player conquers one of these regions on their turn and can hold the region for a whole turn then they receive the token instead.
Vespene - Same again but each is worth two points.
Xel'naga - I see this as really over-powering and would not want to play a game with this in it. (ie. imagine this with amazon or pixies)
I don't see this as any more overpowering than "Were-" since that has the chance to happen more than once (even with Amazons or Pixies). With this power, you might get the power and even then you only get to do it once, you just get more choice of when.
To avoid the excessive dice rolling I'd probably change it to one roll at the end of your turn and on a non-zero roll you get the Xel-naga token. How does that sound?
Zerg - Thematically I quite like the idea of many creep tumors all over the place. They can easily be removed by other players by conquering the region. Again, I don't see this as any more overpowering than say "Commando" which gives you a -1 to attack all the time.
Protoss - Not really fussed about giving away points for pylons. The point of "proxy pylons" in the Starcraft is that they give the Protoss player the ability to attack anywhere on the map very easily but once noticed, the pylon can easily be removed.
Terran - sounds like the trolls?!
It does I suppose. How about each bunker gives a x2 multiplier to defense? 1 race token = +2 defense. 2 race tokens = +4 defense etcetc
Just my ideas on them.
Thankyou for them! I welcome any more suggestions especially as to the number of units each player should get with the races and powers. Cheers!