Get in there. The only reason projectile spam works is because the opponent hesitates to respond to it. You have to weave in and start hitting them so that they can't really keep doing it. The moves that send out projectiles do have a fair amount of start and end lag and you can take advantage of that.
For example with Jigglypuff, her fair tends to be able to easily clang with projectiles and her aerials are great with approaching so you can easily approach by air, get just above them and start with a dair or something.
Luigi I cannot help you with, I don't play him much.
Toon Link's nair and I think fair can clang and don't forget his shield can block projectiles, use that to your advantage. Don't spam them but since you ALSO have great projectiles, use them. Approaching with uncharged arrows both while grounded and short-hopped can put pressure on them to make an advance, at which point you can respond to that.
Good luck and happy Smashing.