Doug, the X10 is roughly as good a street camera as the GRD series. The sensor is a bit larger, but still has DOF coming out of its ears. It doesn't have snap focus, but it's VERY easy to set up for zone focus, and nearly as easy to change the zone with the manual focus wheel. It's just as silent and nearly as stealth. The X10 has more latitude for low light too, and is obviously more versatile. The only thing the GRD really makes notably easier than the X10 (or any other non-Ricoh) is to move instantly between zone focus and auto-focus. That can be a nice thing, but when I'm shooting on the street I rarely leave zone focus anyway.
The GRD is a great street camera, but the X10 doesn't have to apologize to anyone in that regard. Almost all of the street shooting i did in NYC early last month was with the X10. You also have the epl3, no? Another awesome street camera with the 12 or 14 mm lens. Flip the screen up, compose on that, and use the crazy fast AF. The rest of the NYC shots I did with that.
If you dont want to keep your X100, thats another question (I see it's already for sale), but you don't need a new camera for street shooting! You may, OTOH, need a new pair of shoes to go wear out!
-Ray