Okay! I've had TWO other 'starting attempt failures' since I posted this in the last three days and i'm assuming its probably physically the starter.
In both cases I turn the key, I hear a soft click, and then a motor spinning up... WHIIIRRRR.... getting faster as I hold the key in. The engine doesn't turn over even once. I let go of the ignition, give it a moment, and try a second time - then it engages and starts the engine just fine. (so definately not the battery)
My guess is the first time where it repeatedly clicked was whatever solenoid or such makes the starter motor gear connect to the engine, and that it was like trying to get there but just couldn't. Even though that time continued for awhile like two hours despite a few attempts back to back during that time. These last two times it just sounded like it freewheeled. Tho thankfully it was able to start right after.
Does this sound like a reasonable explanation? I'm assuming I should plan to be physically replacing a starter as soon as I can. : P (tho being -20 right now that wont happen for a bit, try to limp until spring more for the moment, or have to pay a shop I guess)