It's a bit sticky because I know I've personally just stopped engaging with the sort of posting and it leaves a lot of vapid thread titles or 'interaction hooks' drifting around. Does it look lively? At a first glance. A second reveals how shallow it is and can very well lose a member if that's all recent activity is. So strategically I suppose I'd want to supplement with more substantial posting, leave the door open for the more spammy poster to interact meaningfully, and subtly try to raise the discourse around it so the spammy posting is an ill advised minority. It's a bit frustrating to get into an exchange if you've seen this a bit and know you'll either get no response or nothing very substantial, so the answer may be to pick up those lost tangents and infuse them with something useful if only to avoid this effect.
Without other errant behavior I'm afraid I'd be too lax on things like warning them or removing their content as 'low quality', I'd hardly want to penalize someone for interacting. I tend to think encouraging what you want is the best path to take but I haven't had to take this issue to its conclusion, so my take is just theoretical.
It's certainly more of a problem as Arantor notes if there is a gamified incentive to just make posts regardless of understanding or interest. I've even somewhat spammy posting AJ itself and through the services where people 'spice up' activity, ie, content bundles. This isn't to say CB posts are usually spammy but the issue and consequence from uninvolved people sucked in to just make posts on a forum outside their legitimate interest can be similar. For AJ, more halfway decent content drowns out the more vapid posting. For sites trying to spice up interaction using bundles, that might be a bit harder without changing strategy to attract more people with legitimate interest, and engaging specifically so they don't wander off to something more engaging.