I took your final "Or gods, for that matter", as a signal that you were using "evangalism" in the looser, analogous sense, to denote strongly held beliefs of any kind (and know you, political beliefs).

The article would seem to support the general interpration that having strongly-held beliefs is stressful on the brain and wears it down, if it weren't for the researchers' specific mention of "spiritual practices and life-changing religious experiences".

They're definitely talking about religion, but actually I would also conclude that it's the stress of having a strongly-held belief system that's outside the majority that "abrades" the brain over time.

So yes, political partisans tend to deteriorate mentally over time. Ever had to deal with an 85 year old rightwing fanatic? It's like pinging a Heechee pouch.