Once the Droid is rooted and has a good recovery image loaded, you can back up and go from "Stock" to some aftermarket ROM for testing a variety of scenarios if needed.
I would recommend testing with an HTC Incredible as well - with that, there's the possibility of switching between Stock HTC build and Cyanogen using the bootloader (requires "rooting"). I'm finding quirks with SenseUI (most annoyingly, the keyboard throwing the same event multiple times) that I would have never caught without the device in my hand.
Also, keep in mind depending on what you're doing, some built in Vendor app (Verizon, etc) might interfere, so testing on a purely stock Google build phone might cause you to miss something.
You have to code to OLD versions often to get huge marketshare due to the fragmented install base so the updateability isn't as important as just buying a cheap one every year or so.