In an effort to resolve my mysterious drop out/distortion problems, I've decided to replace my Roland VS700R(s) with a new Roland Studio Capture. I was wondering whether I could keep the drivers installed for both units (and obviously, only use one or the other at a time) or if I should just delete the VS700R driver and not look back. I was thinking I could learn the ins and outs of the Studio Capture and still work on my clients' projects using the VS700R in the meantime.
I'm running it on Windows 7 Professional 64 bit, fwiw

Congrats! I run 2 Studio-Captures synced together and I really love them. I had a scary driver issue upgrading to 10 from 8.1 but had no problems whatsoever upgrading a desktop from 7 to 10.
I would delete any drivers of any hardware that you don't intend to use. I used to run a MOTU 24io and there was some conflict with the St-Caps drivers. The only other suggestion would be if you intend to upgrade to 10 anytime soon, I would uninstall the old roland drivers as 10 will autoinstall your new drivers and you will avoid the confusion I had when the drivers didn't show up AT ALL in Sonar. I had to uninstall the old roland drivers so the windows 10 drivers could come on line. That was upgrade from 8.1. As I said before, I never had one moments trouble upgrading from 7. I wish you luck and hope you like your SC as much as I love mine.

I have been running a studio-capture for about 6 months and I love it.  I have never had any issues with it.  I think you will be very happy with the upgrade.