Okay, I know that it says that different coins have different effects. I'd like to know which coins do what, and whether it's even worth it to dish out the money for them. :'D Halp, please?

Well it depends on the coin really, they all seem to do Random things. I used a Pink one and one of my pets gained 2 stats (random). I've used a Black before and got a R:97 so unless you get the coin for free (mostly scratch cards) I'd say it's not worth it to buy one.

I've gotten random amounts of sp with a few slots coins but I didn't get very much.

Yeah, slots coins give you between like, 400 and a couple k.

def not worth it then.