Steerer tube length
 

I have 1.5" (40mm) sticking out above the stem. Reason is that my handlebar has about 75mm of rise (reason for THAT is too-short steerer tube on last bike). Aside from the fact that it doesn't look very esthetic, is there any problem with that excess length?

The current setup is perfectly comfortable. My concern is that if someday I get a flatter handlebar, I might need some of that extra steerer tube height.

40mm doesn't seem too long for an aluminum steerer. Check the fork and headset documentation to see if there are any limits for spacers above the stem.

For a carbon steerer 40mm is generally too long. (Many carbon steerers require 5mm above the stem)

He's not mounting his stem at that height. Read his post.

OP: I'd cut that down *maybe* for safety reasons.

What is the safety issue?

I left mine sticking up out of the stem, this is for raising the stem later.

Good plan , threadless headsets don't care if there is a stack of spacers above the stem

just have the top spacer a little bit higher than the steerer tube so the adjusting bolt presses on the edge of the spacer , thru the loosened stem, to adjust the headset preload
I'd use a compression expander on the top rather than digging a star fangled nut into the Aluminum steerer,
if I were You.