It will be a high scoring series, but I don't think Nowitzki will go off like he did in the Suns series. Antoine Walker and Udonis Haslem showed during the Pistons series that while alone they are not great defenders, together they can slow down the other teams forwards.
The only game I saw where the Heat's frontline (besides Shaq) got dominated was game 5 where Tayshaun Prince got 29 points.
I expect around 23-26 points a game for Dirk. Basically around his regular season average. If you don't cout the abomination in game 4 when he got 11 points, he's averaging 33.2 points a game. He won't do that against the Heat. Also, he won't bust out for 50 like he did against the Suns in game 5.