I agree with you spiral, that Damp is by far the superior center. But I think his recent success can be attributed to two factors, both of which suggest that he should continue to come off the bench:
(1) Someone else touched on this, I can't remember who (if you happen upon this post please feel free to credit yourself) - Officials have a tendency to be more whistle-happy in the beginning of games. One of Damp's biggest problems in the past was getting into early foul trouble (silly fouls, off illegal picks, unnecessary touch fouls in the paint, etc.). This prevented him from playing aggressively in the beginning of games and would often set the tone for the remainder of the game (we've all seen that a timid Damp equals an ineffective Damp). By bringing him in off the bench, Damp has greater flexibility to really play his game - no worries about fouls, just focus on getting rebounds and being a big body.
(2) More obviously, by bringing Damp in off the bench, AJ is playing him against the opposing team's bench players. While it is debatable where Damp ranks in terms of starting centers, I guarantee you he is the best of the best in terms of "back-up centers" (I use the term very loosely). By playing against 2nd-string opposing big men, it is much easier for Damp to exert his will both offensively and defensively, and we've seen his numbers jump substantially as a result. Furthermore, if he's in as part of the second unit, he can get alot more touches (something Damp has talked about in the past, the more touches he gets, the more comfortable he is and more in tune with the flow of the game) than if he were in at the same time as Howard, Nowitzki, Terry and (insert 2 guard). Also, it's worth noting that Stack (as the leader of that second unit) has worked well with Damp recently in terms of getting the big guy touches. Diop doesn't need touches to be effective, which is why it might be better if he starts.
Finally, I think it is a question of Damp's mentality. Again, if he's comfortable, getting touches, and doesn't have to worry about fouls, he will be alot more effective. V2M has a point in saying that the current system has worked well - if we start slipping then I am 100% with you that one of the first moves would be to reinsert Damp back into the starting line-up. For the time being of course, 95% winning percentage can't be wrong!
