Just by looking at your times (which are better than my own PAL Non-NBT records for this track) it looks like you already have mastered the correct general route through the course. Once you get to the 1'30"00 barrier on BC1 PAL Non-NBT, all you can really do is make each corner as pixel-tight as possible and avoid brushing against walls, Thwomps, or the yellow bumpers. I'm afraid there is no easy way to improve your PRs beyond this point.

About the only tip I can give (which you probably already do, given your current PRs) is to start turning the Kart to the right before you jump over the last of the first set of bumpers, which will help you cut really close on the track's only right turn. Do the same for the final turn, only to the left, and always cut to the inside of the Thwomp. If you hit this Thwomp and mess up a run, you weren't taking this corner sharp enough anyway.

As for whether or not to boost here, you probably shouldn't bother with a boost on PAL Non-NBT. It may be worth trying on NTSC, though. It depends on whether or not you can get a drifting line in which you do not lose so much time from taking the corner wider that it cancels out the time gained by the brief speed boost...