He'll lose only a few from his base (most will hold their noses and vote for him come election time), and he'll get a few new Hispanic votes, but not enough to make a difference. You're right, Hispanics will still overwhelming vote 'Rat regadless of what Bush does.
Vote pandering is usually aimed at the center of the political spectrum, and if polls are any inidication, the majority of the center is staunchly against Bush's proposal. Either the WH miscalculated or there's another reason for this. Perhaps it's political payback to campaign contributers whose businesses desire cheap labor in return for filling the GOP coffers. ......Many possibilites exist.
I think Bush stands to lose more than a few from his base. Judging by some recent conversations I've had with friends when the subject turns to Bush you can feel the Rage. My Dad surprised me the most. He has voted straight ticket Republican all his life and the Amnesty business was the last straw for him. Just today I was talking with a friend who voted for Bush in 2000 and it didn't sound likely he would be doing so this time around. I've heard similar responses from a lot of people in the last few months.
Of course it's not just the Amnesty Fiasco but the whole Inane Bush Package of Uncontrolled Spending, New Monstrous Entitlements, Promotion of UnFree Trade, Outsourcing, Pandering to minorities, Failure to protect our borders and control immigration etc.
There is conservative backlash developing against Bush and it's only going to build in the coming months IMO. Throw in a economic calamity or some other "event" and Bush could find himself in another horserace of an election.