Angled tips are helpfull when you cartwheel a plane (You'll only do that once with your JBB anyhow) so don't bother.
Building new alirons is kind of a big step (and may not help).
How old are your servos? MG servos get slop kind of quickly sometimes- replace gears.
The control arms on the alierons can also get sloppy after time. easy to replace if the hole is woollered out.
And already mentioned seal the hinge gaps.