I'm the author of the original IPB (Invision) stopforumspam plugin and it's been running for 7 years now without any need for an update and the last 7 years only 2 spambots made it through (out of ~20 average registrations per day)
I can recommend using at least IP and email matching, both registration and login. It creates very little overhead.
Ive deleted four in the last two days, we seem to go through a phase of getting quite a few at once then nothing for months and months. All we can do is keep our eyes open and report any as soon as you see them , then its up to us spam gunners to blast them out of existence !