I don't know much about the Overdrive but it sounds like so long as you have the latest goods which you do, you can pretty much do most the rest that the newest offering provides. Or, if you sold the OR4+Monolith and the Overdrive sounds better, you may just consider leaving it like it is or simply doing the "basics" like the Hynes USB (specific areas that have been updated and "clearly" prove a substantial difference). I think once you get past the OR4+Monolith, you are in a darn high end enough league where the simple/basics is what I'd advise vs. going full blown/modded. I do love having it all, but at the same time, I know audio is compromises, so I always go with what I know works (in this case your Overdrive you know works as it does), and then maybe a couple little upgrades that are not costly, but are supposed to have the most dramatic affect on the sound all in all.
Cheers!