I can see two things that will force a change to aluminum rims: damage to the existing tires and minimal availability of a good 27 inch tire, and damage to the existing rims or inability to true. If you go to aluminum rims (and I don't deny their benefits), you'll need new spokes, tires, and rims at teh same time. You should be able to find a decent set of 700C clincher wheels used for less $$ than a full wheel re-rim.

I think this is how Frankenbikes are born!