Good news. I was able to reproduce initial CPU hog on my machine.
The problem was caused by my TotalFinder starting in dual mode and having “All my files” in the right pane. Under some circumstances Finder is updating icons (and metadata) of this long list of files several times a second and this causes TotalFinder to re-apply sidebar mirroring hack multiple times. This alone would not be a problem, but this rapid queue of update requests caused an infinite loop of TotalFinder updates - in other words: my code touched some Finder views and this scheduled another update, which in turn touched some Finder views, scheduling another update => ending up in infinite loop of updates.
I’m working on a fix. This weekend I should have a new beta release out. Hope this nasty issue will be a history.