If you can get away with removing 2mm of spacers on each side of the wheel (which means that there are already unnecessary spacers on the drive-side), then perhaps you should do it. But using an 8/9/10-speed hub at 126mm spacing usually means it's really, really dished so you have the non-drive-side spokes way more loose than they should be; not advisable if you don't want to start breaking spokes.

I know that in principle aluminum shouldn't be flexed like this, but in practice tons of people in the mechanics forum do this and seem to work out okay. Nashbar actually makes an aluminum touring frame with 132.5mm spacing so it can be used with 130 or 135mm-spaced rear hubs.

I think you have a much greater chance of breaking spokes with a 126mm-spaced rear wheel than you do with flexing the frame 2mm on each side to fit the wheel in.