DrPaul, I agree with your line of thinking, and your choice of cars--that E31 850csi of yours is stunning.
And as far as engine modifications go, chips, intake, exhaust, etc., I believe I've reached the edge of the ROI/cost effective envelope. Unless somebody comes up with something spectacular, with measurable results, at reasonable price point (Steve D., are you paying attention?), I’m pretty happy with the mods I’ve got and the performance they give me.