Also, the earnings display seems random in that it goes from seemingly too little for the time spent mining to a significant increase, which I presume is just something catching up somewhere.

"Pending Rewards" is only rewards from people buying equipment, you will not see the daily emission earned for owning miners as pending rewards as it get distributed the same time pending rewards get reset. You will see pending rewards + emission rewards as your "past rewards" which are your rewards from the last payout.

I stole the GPU pool, and spent about 100 STEM to boost into ape mode, but the bar never moved.

The bar moved but the larger pools require more boost. They are meant to be boosted as a community effort.

The cpu pool is showing only .001 pending rewards while the gpu pool is showing a little over 10.

This means not many CPU units where purchased that day.

Are these bugs or features?

It's how the game works.

My request is simply adding a mouseover display to show how much STEM is required to achieve the next boost, unless it was intentionally left out for a reason.

The progress bar shows you how close to boost the community is.

Also, I'm curious why you chose STEM as the burn token.

STEM is my token for STEMGeeks (Science, Technology, Engineering, Math).

Are you considering doing one of these for other tribes or incorporating other tribe tokens into this one?

No.

I don't know why we shouldn't have one of these for all of them. :)

All of them are not my tokens. Any game I create I plan on encorporating STEM token in some way.