Should Smart Directors Go Commercial?

That Fuzzy Bastard has what I think is an extremely fair critique of my excitement over important directors who make big, B-style projects.  He writes:
In my usual capacity of curmudgeon... I'm actually sort of unhappy that so much of Hollywood's output is about "really excellent directors handling big, pulp projects." I think one of the really sad development in current Ain't-It-Cool-ized Hollywood is that once a director establishes him/herself as an important artist, the next step in advancement is... doing a pulpy action movie. It's the takeover of the B-pictures, creating a world where successful Hitchcok would have gotten stuck doing The Creature From The Black Lagoon and North By Northwest would have to be made as an indie movie. David Fincher has done some really smart, interesting films, and I'd like to see him continue to make more thoughtful, adult pieces rather than an F/X flick where a boat fights a squid.
I suppose my response is as follows: 1) I think B-movies and more unconventional narratives can coexist, and I'd be happiest in a world where they got equal billing.  I also think that ultimately they can reinforce each other: if folks get to know David Fincher, for example, through a big, fun, commercial picture, they might be more tempted to give one of his more personal projects a shot.  2) Getting good directors to do large commercial projects gives them a chance to play with their personal style without intense concerns or constraints about whether a project will make money.  And encouraging folks who have highly developed sensibilities to take on big, generic, commercial forms means that those movies will actually end up looking and feeling much more differentiated than they would if they were all directed by Michael Bay.  I totally agree that it would be bad if folks like Fincher abandoned their unique visions to make money.  But I don't think it's tragic if he takes a temporary side trip into something big and fun.