So wouldn't over or under voltage on the NVRAM apply to SRAM as well if R11 was out of spec? In other words, upgrading to NVRAM doesn't cause the modification to be any more necessary than when factory RAM was used.. other than there's a chance of voltage going out of spec on a $15 nvram chip versus a $2 RAM chip.
I don't think people without tools or experience need to be too concerned if their R11 isn't looking toasty. Personally I'd view this as -- if your R11 is looking brown or otherwise fatigued, definitely think about replacing it or doing this mod to get rid of any heat or out-of-spec voltages. If you can't do your own board work, at least periodically check it. If it's a machine that will be on 10hrs a day somewhere.. just pay someone to do the mod or replace R11.
Not disagreeing about the usefulness of the mod. I just think some people may get the wrong idea that it's inherent to upgrading to NVRAM because that's when it's being discussed as a recommended mod, when really it's a problem with an aging board and fatigued R11 that will affect *any* early Bally/Stern MPU regardless if it's using RAM or NVRAM.