USB 2 is still pretty new, so choice will be limited and probably more expensive. Don't forget all USB 1.0 printers will be compatible with your USB 2.0. You can always upgrade when there is more choice.
Don't think so because of the finite time for the actual printing process, whether jetting the ink or spreading the toner or whatever together with mechanically moving the paper/printheads and so on. These are VERY slow in comparison with the operating speed of even USB1.1 that it does hardly seem worthwhile to promote to USB2.
jazzypops suggestions don't alter anything I wrote and just because these printers have this capability doesn't mean that they work faster. It may be that you have to pay extra for a USB2 facility that doesn't do anything. If there is no on-cost then obviously no problem!
I've recently purchased a HP Deskjet 6122 which is USB2 compliant. I only have a USB1.1 board but everything works fine and couldn't be happier with the printer, even comes with an automatic duplexer for saving paper and creating clever docs.