I've just had exactly the same problem - new hard drive, so re-installed Windows 7 (64-bit professional) and all the drivers from Dell Downloads. WiFi worked, sort of, but after hibernation would always require a wireless card reset through "troubleshooting".
Anyway, thanks to your observation about DW1501 versus DW1530, I have now solved the problem. It would appear that the drivers that Dell list for my E6420 are for the DW1530 wireless card, but the wireless card in my machine is the DW1501. I instead downloaded the wireless card drivers for an E6410 (which say they're for the DW1501), uninstalled and deleted the "E6420" DW1530 drivers, and installed the E6410 DW1501 drivers. And hey presto it works perfectly now!
As far as I can tell, the Dell support tools, infrastructure, and website are next to useless at indicating which drivers I need. The "scan your system" (or whatever it's called) apparently can't even detect that I'm running Window 7, not XP. And its recommended driver list is not affected by me installing / uninstalling groups of drivers.
I wonder how many other drivers I've installed for my E6420 actually aren't for my machine!