Before spending more adding ceiling insulation material, which only bounces interior heat downwards, why not take time and perform a crude energy-audit with a cheap $30 Harbor Fright infrared thermometer?
Your bills are pretty low for now.
You have time to think about it.
Over the next year during the coldest and hottest months: check the walls floor and ceiling and note discrepancies.

Adding more material in the wrong spot might equate to zero additional benefit.
Or it cause problems later on.

The unconditioned attic space might only need more passive/active airflow.
Most ridge vents are very insufficient from what I've heard.

The attic portion of the garage has a full length ridge vent and a gable vent on each end so I don't think I can do much more for air movement. The walls are enclosed/insulated so nothing more I can do there. The garage door is a brand new insulated door so nothing more to do there. The only area I can improve is ceiling/attic insulation. Not that much cash to blow 20 bags or so in the attic.

About 10 years ago I cleaned out a Lowe's parking lot clearance sale for track lights. About $5 for a box for a set of two and railing. Bought a bunch, and use them whenever the project calls for it. I just attach the rails and make tracks as long as needed.

Like a squirrel hoarding acorns, I have proudly hauled along my "big gay track lights"(as my friends like to call them) with me through the years.

Only drawback I can see is that (like mentioned), the light is dramatic and pretty, but not as useful for practical work in the garage, and changing the bulbs is a pain when they go. Also, they also attract spider webs, and the white ones will slowly discolor over time to a not so fresh yellow ochre hue.

I use them for closet lighting and they work great. The ones in my garage display my woodchipper like a guitar on stage in an MTV unplugged concert. The table saw and it's sawdust looks righteous. Everything else is pitch black. I need to change those when I get around to it.