I don't think it's unplayable, but it would certainly make things more fun if the vaults were a little bigger. Personally I think the vault quests should have gone something more like this (considering the cost). SH I + 1000, SHII + 1500, SHIII + 2500, SHIV + 4500, and SH V + 8500, which would put you at 20,000 total with a SH V Vault. I was really kinda hopingforsomething betteron the vault caps considering it cost meover half a gold to go from SH III to SH V.. and I only got +400 bulk for that.
If not better vault space.. how about adding another cargo disk slot?