FACT #1
+Power Stone Chance Statues do affect Dr. Terror and Lt. Hammerman.
Both Terror and Hammerman levels have some pre-defined Power Stones which you'll get every time, but on top of that there are the regular random drop chance Power Stones which +Power Stone Chance Statues will improve your odds of getting!
FACT #2
Every building (including destructible barrels) has a 2% chance to drop a Power Stone of some sort, and the HQ has a 25% chance. Fragments are the most common, Shards are a bit rarer and Crystals are the rarest.
Example: +100% Power Stone Chance = 4% per building and 50% for the HQ
So if you're super lucky, a base with 10 buildings could give you 10 Power Stone Crystals! And if you're unlucky, it could give you none!
FACT #3
All buildings are always destroyed when you successfully raid an opponent (either by yourself before taking down the HQ, or whether they self-destruct afterwards), so your chances of getting Power Stones are equal in both cases.
FACT #4
"did you mean the outcome is pre-determined at the time we clicked Attack a base and regardless whichever buildings we destroyed, the amount of power stones, we are going to get, is the same." - minhp
No, the outcome is not pre-determined - the dice are rolled after you destroy the HQ.