I'm not sure what 'advantage' you are trying achieve wanting to use a fresh basetape after every repair, but the basetape doesn't need to be supple? In fact once the glue dries, it is hard anyway which is what you want. You don't want the basetape to 'squirm' around on the rim, you want a superglue type bond really? When people talk about supple tubulars they mean in the sidewalls & tread/carcass really.
Indeed but the base tape needs to be supple and flexible to get the fit and seating correct from the outset.
As for contamination in the basetape, I don't know what might be causing this. As far as i'm concerened, you just wipe it with a some solvent to remove any surface grease, apply a layer of glue and fit it back on the rim. The next time you remove the tubular, you repair it, coat it with a fresh layer of glue which dissolves the old dried layer, flattening any lumps and you then, fit the tubular and job done. Inflating to max PSI squeezes the glue level again anyway.
There is also the other concern which I have hinted to. I bet you once a tub has been removed more than two times it has some or the other form of permanent contamination in the base tape. That is a reliability issue which can be avoided by a complete overhaul/replacement of the base tape as should be done.
In addition, if the base tape is not fit for purpose gaps in the contact between the tub and rim start appearing. This further induces contamination of the base tape.
I read you.
I'm kind of a mister perfect myself but there's a fine line between perfection and mere paranoia.
You notice a hop in that tubular and you know it's caused by too much of that old rim cement?
Give that basetape a good scrub with a brush dipped in White Spirit so that hardened glue weakens and conforms with the rest of that rim again.
I'd only recommend this as a last resort measure for an already desperate case.
These chemicals may well do more damage elsewhere than you'd wish for...
The problem you're experiencing is likely caused by using rim cement that's on the brink of chemical stability.
This creates random spots of very firm adhesion with weak spots inbetween.
Stir the rim cement well before applying it and you may well be out of the woods..
Other causes are to be found on the other end of the stick. Contaminated basetape or a not so clean rim for instance.