Naptha isn't very clean. You will want to use acetone or a hot strong detergent to clean the rims before using glue.
I don't have an anecdote for you but i think most will accept that some glues don't play well together. The trick is knowing which glues need to be kept separate, and there's nobody who really knows this information as far as I can tell. So the prevailing wisdom is to just remove the old glue. Cuz you don't want to suddenly be tire-less when you come off the banking at ~40mph (or faster, depending who you are). That could hurt.
As far as your other question about how much glue build-up is too much: I've been told there is a point where too much is bad. I've only rolled one tire in my life. 1000 years ago in a crit (think down tube shifters, non-ironic mullets), a guy went down in front of me mid-corner. As I was sideways trying not to hit him and go down myself, another guy T-boned me. When I picked myself up, my rear tire had rolled. There was a lot of glue on that wheel, and that could maybe have been part of it. Or it could have been that impact while the bike was sideways levered the tire off no matter much or how little glue was on there.
Too much glue is probably bad, but too little is maybe worse. The right amount is probably..., enough. Are you looking for a gluing primer? There was a good one on the FGF page, but that page seems to be inaccessible or booby-trapped or something these days. Probably Carleton can scare one up, might be a useful sticky.
Try the following for a link on glue procedure complete with adhesion tests of different glues and procedures.
Summary is 2 layer on the tire, 3 on the rim. The rolling resistance tests have also shown this to be better than less glue.
Goof off works the best of anything I've found (don't use the latex paint stuff, they make two kinds) on Mastik. Well ventilated area, voc mask preferred, and chemical gloves. I use paper towels soaked in the stuff. Make a pass, then let it sit and soften. Scrub as it softens and it rolls off. Really old stuff use some Scotchbrite pad soaked in Goof Off. That's for carbon rims. 10-15 minutes per.
On aluminum rims use a brass wire brush on a bench grinder. 5 minutes or less.
I always clean the old glue off. You're looking for as much surface area contact between the tire and the rim to lower rolling resistance and maximize adhesion. Leaving old glue does a lot of bad things, but probably number one is you end up with a lot of surface area voids.
Yes, you can half ass it and leave the old glue on, but it won't match what you'll get with a clean rim and tire.
Depending on the tubular and rim I'll go 2-3 coats. Mostly two on the rim and coated base tape, add a third coat on bare tape. Use a foam brush for the rim and an acid/flux brush on the tire. Do it right and you should have the base tape sticking to the rim when you remove the tire. This means you>factory and that's the goal.
You'd think that someone would have developed a superior system than sew-ups with glue glue or clinchers by now.
Problem for track is that we run ridiculous pressures that for now only a glued on fully encased tire is going to be able to sustain without bad stuff happening.
You figure 200 MPH 2000lb Daytona sleds are fine on tubeless, but they aren't counting grams or trying to build tires you can change on the side of an MUP.
Zero doubt that it would be pretty easy to design a tubeless tire and rim combo for track that could handle 200 PSI and laugh. Also no doubt that you'd be a laughed at during the venture cap presentation:
"Now I think we can move 300 units a year..."
I did a bit of a BMX stuff during a crit over the weekend on them...made me smile.
I'll be glad when tubulars die. Tubeless sound promising. Maybe someone figure out how to use them without goo, or at least without so much of it.
The conversions still need sealant though. Some of the other systems like Bontrager's road tubeless also need it...I think anytime there's a liner involved that's going to be the call vs. a solid rim.