If working properly, that bike, steel rims and all, is easily good for 20 mile rides or 100 mile rides. If you are up to it, the bike is perfectly capable.

I personally might not spend much on aluminum rims, until you ride the bike with both brakes present and properly adjusted with salmon Kool stops. I think you'll find it stops fine in the dry. In the wet, it won't be as good, but you might as well see how much riding you do in the wet. If you find that you do ride enough to want, need, or be able to justify a fancier bike, then buy a fancier bike. This is a good, solid, nice-looking bike that may serve your needs just fine.

Anyway, used wheelset with decent aluminum rims will cost $80-120. Add $100 and you'd have a $200 bicycle. Which will come with a decent aluminium wheelset plus a lighter frame and more desirable components. You can buy all those upgrades much more cheaply as part of a whole bike, than buying th one by one.