There has been some concerns on how bumping can be abused to garner some extra reputation. I'm going to question the opposite. A scenario where not bumping can be abused.
Today of all days, a post was reported by Smoke Detector in Charcoal HQ and while it was obviously spam, it was deleted so fast by its author that it seems no one could kick in a spam flag. All good, eh?
Except undeletion doesn't bump a post, so said spammer can easily evade many eager eyes by undeleting it when we're not watching. The post will not be bumped, it wouldn't be caught by Smokey, and it will likely remain unnoticed for a long time — much longer than spam on AskUbuntu usually remains.
Notably, deletion has been used to stay safe from mod-hammer for longer than it should've been, so it's not far-fetched at all that a smarter spammer use it to spam even sites that are good at handling it.
While we're biting our fingernails and trying to find out whether this spammer was too stupid or too smart, we can also discuss what we could do about this "exploitable loophole". One user in Charcoal HQ proposed that undeletion show up in SE's real-time tab, which would be something Smokey watches.