"The things I know I'll be able to tell the difference are with my pedals, seat and tires."

Yup, I think you are right. Wear down those tires, then replace with some good 23c size rubber from probikekit.com. If the saddle doesn't suit you, replace that, too. And you already have the pedals.

Seriously, though, if you are just getting back into riding, some good apparel -- including stuff that allows you to ride in colder weather -- will make a big difference.