That's right...even now, when the car really isn't worth much, I would be devastated if someone took it. We've already put in enough work to make it valuable to me!
But I have considered removing the radio and putting it away somewhere...it's worth $150 (if it works...and it can be repaired.)
Unless you get targeted by someone knowledgable about old bug radios, who is looking for that radio in particular, most people who break into garages are looking for power tools that are worth more than that radio, really. No pawn shop is going to pay what a collector would for that radio.
But if you'll lay awake worrying about it, then certainly put it somewhere safe :~D
There's lots of little security gizmos that work pretty well... and some that don't. One of them that's pretty handy is a little battery-powered door-hanger that you put on the doorknob.
If the knob gets rattled it goes off. Squeals pretty loud. Between $5-10 at a hardware store.