You won’t get any more spam using this system than you do already, provided you don’t start throwing these tagged addresses around the web willy-nilly. In this respect, this isn’t comparable to a catch-all in any way. With a catch-all spammers don’t need to know your exact address to spam you. With plus-addressing, they do.
Not to mention that plus addressing is very, very old and very common. I’d imagine any reasonably smart spamming software is capable of stripping off this suffix. It’s great for sorting mail but doesn’t do much for spam filtering.
If you want useful replies, ask smart questions.