Nothing wrong with being in the minority, especially when you've got a sound plan in mind. There are some highly-experienced members on this board who dislike the folding bars. To each his own, I reckon. You're coming at this with some clear goals, a systematic approach to modifications and willingness to change things that don't work as well as you'd like...that's an outline for success, imho.
Initially, I missed the fact that you had changed-over to a Chinese front end assembly; that does make a difference and it mostly has to do with the bar clamp/bar tab interface. I still think that the self-loosening handlebar knob issue could be solved. If you can live with fixed-position handlebars, blue Loctite & fresh lockwashers ought to do the trick, and on the cheap.That said, one advantage bmx bars do offer is fore/aft adjustability, something that's not possible with the OEM-type folding bars.
The CT70 seat is an odd duck among bike seats. That center hump, required for structural strength, also leaves the foam padding ~1" thinner in the worst possible place. I recommend using a makeshift cover so that you can test new foam configurations on the seat-of-the-pants dyno...literally...before committing the changes to vinyl, or leather. IDK, your type of usage may make seat comfort less of an issue than it is for a hardcore road rider (like yours truly). I can tell you, from firsthand experience, making one of these seats comfortable and visually thin, is anything but easy.
As for wanting to retain most of the stock(ish) lines of the original, while upgrading/changing things, does this strike any familiar chords?