With a band like Clutch I don't know if I would go say their sets are getting stale, when the sets are so different I don't know how they could be stale. Its basically a luck of the draw. Granted since ER came out its a bit much playing all of your new album at a show. But even at that they haven't been doing that every night since it came out.
I don't think there's such thing as a predictable encore (especially comparing to Megadeth). I've been to shows where Mob isn't played or its been the opening song. EW/1ED does need a break. Out of the 10 or so times ive seen them since that came out its probably only not been played once.
Dont think Megadeth could function now if they opened w/ Peace Sells or Holy Wars (yes I know they used to do that years back).