Pools are a mess.
Imho the the idea of "investing" in a pool seems rather daft. The restriction of only 5 or so supplementary pools (epic + pools) is more than enough to prevent people from picking loads of great powers.
On the other hand, why would anybody pick the crap powers if they weren't forced to? Why not just pick the 5 best powers from the pools?
If there are pool powers that are crap, why do they even exist?
All this considered, it seems to me that one solution is to;
bin the "you must have already got X powers in this pool" restriction,
replace the pool powers in question with ones that people might want.