As CHRles was kind enough to demonstrate, the signals actually do compliment each other. And, Kiss 108 isn't exactly "loud and clear" in Portsmouth itself. Yes there are some places around the Port City with decent reception of Boston signals - but downtown is not one of them. It faces north toward the river and Kiss 108 doesn't come in well at all. Now it does, thanks to the 95.3 signal.
Basically, CC gets their popular Kiss 108 brand into a fairly affluent area where there are quite a few commuters into the Boston area. As the 95.3 signal has NEVER been successful, there's nothing to lose and a lot to gain here with a simulcast. I know that it's not at all in the spirit of local radio - but none of the alternatives would be either. And, given the small signal, I wouldn't see CC hiring a bunch of live and local jocks to staff it.
Sadly, this is about as good as the CHR format is going to get in this market. And, it is an improvement over the very AC-leaning WERZ. Perhaps there's a little cannabalization, but probably no more than Kiss has in Boston with JAMN. And that monopoly has worked quite well for them. They're probably pulling a page out of that book when it comes to their Portsmouth cluster.