I get that nuking the thread absent any solid proof might still be seen as drastic, so how about temporarily locking it for, say, 7 days, or until the OP cleans up all the spammy posts?
Even if he deletes all the spam from bump bots, the goal is still accomplished: the thread stays on top thanks to the spam.
Yes, I imagine the bump bots will continue posting even as the OP is deleting. I'm not really seeing any downsides to temporarily locking the thread, then. There has to be a smarter way of dealing with this rather than individually deleting posts or banning users (however much both may be deserved). I mean, a mod could literally spend all day on that Roomdao thread and only tread water, so to speak; the spammy shitposts begin on page 1 and continue, unrelenting, for the next 170+ pages...