Is it going to be worth replacing bat insulation with rigid foam between bedroom and garage?
Rigid foam, no, not unless you airseal it. Spray foam, yes. Assuming you define "worth it" as valuing comfort over money. ROI is 10-20 years for just about anything in HVAC, if ever.

I'd pull the drywall off the ceiling in the garage, not pull up the subfloor, unless it was being replaced.

Ridged foam in the attic might be easy to install and do something.

Someone who knows what they're doing might say no matter what the insulation, you have insufficient airflow. I'm going to guess all three: above a garage, below an attic, and longest run from the furnace. Bonus points for unideal sun exposure (get better drapes).