Probably just as easy to get the originals straightened - certainly cheaper. My chap charges me £12 a rim for full service/tighten/etc. Where do you live?
Replacement wheels - modern stuff will often have a wider rear spindle/axle, which will mean cold-setting the rear forks to fit (bending it using a bit of wood basically, surprisingly easy to do).
Then there's the potential problem of cassette type rear cogs - most, if not all, modern 700c road wheels will be cassette type hub, whereas the Dawes may have screw-on type hub. The difference being is the rear cogs slide on, and are then held in place on the hub by a collar, whereas the screw on type screw the hub face. - tricky to explain without photos.
If you're going to ride a roadie down stairs, just get the steelies straightened and then stick with them. They'll warp easier than alloy rims, but you'll get far more corrections out of steel than aluminium.