Are you suggesting we promote spammers to boost activity?

Personally I think the best way to avoid spambots is to implement some custom verification algorithm. Although it is difficult to achieve, it should provide the best results. Captchas can be easily broken and since most bulletins and probably other boards use the same system, it's relatively easy to create a generic algorithm to break them all at once. Now imagine if every forum used its own system... the odds would lie heavily against the spambotters as they would have to circumvent the verification separately on each and every board to be able to spam.