Hold off to find out if they are going to keep the unlimited data plans for 4G phones on 3G networks.... and see. I suspect you'll know the answer in a few weeks. I'd definitely wait for the new phones; love my Droid X, but a Droid X2 sounds even better (for 3G); and the Bionic looks great.
My next upgrade availability in in July, and I will be waiting for a dual-core 4.3" global phone (because we are going to Europe in the summer of 2012), plus since I've gone to the tablet, I have been less enamored with my smartphone, so the need for instant gratification has subsided a bit.