There are modern freewheel type wheels that you can get made by Weinmann, but if you were really interested in getting new wheels, you might consider building them yourself with vintage, high quality hubs. That would probably run you $200 a pair for a decent set. I'd probably keep what you have though, unless mismatched rims were a significant eyesore.
Weightwise, 21lbs is quite respectable. Dropping weight however will usually require changing the wheels. There's not a huge savings to be gotten from changing a seatpost assuming you already have one that's aluminum, and decent. You could try changing the seat to one that's lighter, but shedding 400 grams off a bike is much more pricey than losing 400 grams off your own body.
Edit: Also, everything Robbietunes said.