Perspiration: Hoodie, track pants, extra duvet... woke up a little tiny bit moist, but not that "sweaty," really.
Symptoms update: I feel a little better overall, but I have a headache and the cold has now gone down into my chest. The sore throat is mostly gone.
Somewhat baseless hypothesizing: It's hard to say if the change was because of the sweating or my body's natural reaction — colds change anyway — but I don't think a sweat-a-thon would necessarily do any harm. If you think about it, that's what fevers are all about: your body is trying to make life miserable for whatever pathogen has invaded, so if you pile-on the blankets, you're helping out, right?