Mods use tools to moderate. Ok. You want to have a little hobby of moderating a community. Fair enough, pay for your hobby. If not. Let Reddit fix the spam problem when it becomes a problem, because it will become a problem and Reddit will be forced to fix it because the users will hate it and it'll harm growth. If not, pay for the software to do your little hobby.
Actually, I think this is one point where Reddit could score some good will points by letting moderators use the API for free to access the communities they moderate.
Personally, I would. But they announced that they're working on their own tools to improve it so maybe they're literally just going to provide all those tools for free. Who knows.