Yes, I think this is a good idea. I think it may help you to recognise better, in time, what is spam and what is not. The only downside is that you will probably delete new members who are not actively posting but are browsing the forum topics to learn and get a feel for it first before posting.... which may take some time. At the end of the day though, it is no problem to re-register and this is
a real problem which needs to be dealt with.
To help you, would it be a good idea for new members ,on registration, to insist that they send you a private message just to say 'hello'...you would then know they were real people. Create a list of those people who joined and notified you in the last month and cross reference this list against the names with just 1 post on the boards and delete those not listed....most likely to be the work of spam bots. Alternatively, create a new area for people to do this, that you can check on periodically, if you don't want your PM box flooding!
The general idea I'm getting at is to get REAL people to do something that spam bots can't do thus isolating there work for easier identification.
May be it would be an idea to have a prominent and permanent discussion thread on this subject, after all, there are a lot of highly intelligent, creative and resouceful people who frequent this forum and this subject may trigger their interest and desire to contribute if it passed in front of them whilst browsing. If anything it would help to raise the level of awareness and responsibility amongst members about spam, instead of struggling on the subject by yourself.