I'm personally not a fan of the fact that creeper blasts don't do damage and tnt and ghasts. But I see how having this gamerule on can cause problems with griefing and such. However, turning it on in the nether and/or end would be really awesome.
I don't think you can set it to be dimension exclusive
Yeah, I'm not sure either, but I figured it doesn't hurt to ask.
I know SOME multiverse plugins support it, but I don't think WoA has the one i'm thinking of