Bush Signs Bill for Rosa Parks Statue:

"The provisions that expire, in 2007, include one requiring states with a history of racial discrimination _ mostly in the South _ to get federal approval to change their voting laws or district lines and another requiring election officials to provide voting material in the native language of immigrant voters who don't speak English."

I see two reasons why Bush wants to renew the voting rights act. 1) He's a decent fellow that's really unpopular with black folks and he wants to do something about it. Another way to say it is that this is part of Rove's long-term GOP plan to chip away at one of the Dem's strongest pillars.
2) He wants to keep a Republican DOJ in charge of approving districts. See the redistricting of 1990 and 2000 to see the damage a GOP led DOJ can do to Democratic House seats.

While this does increase minority representation in the House, they seem to demolish Democrats. When I lived in Georgia, the Bush, the elder, DOJ crushed the Democratic Georgia delegation by flipping the representation over to the GOP. By the time they were done, their were no white Democrats in the delegation.