Personally I don't think alts should be IP banned. If someone wants to put all this effort into making *t, let them... On my server, the top 2 player has a 35k power alt, and the top 1 player has a 36k power alt. If they want to put so much effort into it I don't see why they should be punished...
If you have spies, there are ways to root them out, like placing a level restriction on group members or watching for people who enter for a few seconds and then leave ^^

lmao xD I don't have *t personally, but several friends of mine have alts and I know they play on them just as regularly as their main accounts. some people even put money into their alts and it'd be unfair to everyone who put effort into alts to ban them

Doesn't the whitelist function in 2.0 update fix the problem of spies? I could be wrong but that's what it sounded like