Hi BFG_29! Each unlocked Town Skin constantly gives you bonuses regardless of whether the Skin is activated or not. The more Skins you have, the more bonuses you get. Please note:
Have a nice day!
I think a similar question to this was asked before so can only imagine it's the same deal.
You can search for the thread, but am pretty sure the answer was along the lines, that the bonus only applies to those that have it, its hardly going to be a 'cover all' unless they didn't think about this when programming.