I'm torn. The partisan Republican side of me would love to see Dean fail, in part because I think he's more of a threat in the general election than generally perceived, and even more so because I believe you are right: If Dean gets the nomination he'll attempt to purge the clintonista toadies from their positions of power within the party, starting with McAwful. This may make the Dems even weaker in the short run, but it is the necessary beginning of reform and rebuilding for the party.
My Republican side, however, which would love to see the Dems remain mired in clintonite corruption and counterproductive power-grasping, is overruled by my American side, which would prefer reasonably responsible parties on both sides of the isle.
God help me but I gotta root for Dean, and eventual 'Rat reform (even if it has to go through an ugly faze when it moves even further left). In the long run the Republican party will also fall into ever deepening corruption if it doesn't have responsible and creditable opposition.