I never did get around to visiting the doctor regarding that big icky red spot on my toe, but it turns out that everything is OK. I was taking off my shoes and happened to notice it was a different shape. I looked closer and realized a piece of the "spot" had rubbed off, and the rest of it was white around the edges, like a scab. I poked at it for a minute - not too roughly - and bits of it flaked off, revealing happy normal pink skin underneath.
There's two little residual flakes I didn't manage to scrape off, but they'll probably fall off in a few days.
So hooray! My toe is back to normal! It only took a month for that blood blister (or whatever it was) to go away on its own.