I commute in about 11.6 miles each way into central london. Im normally quite hot and sweaty on arrival. What I found was that my top is the most sweaty actually, I find that my shorts don't really feel damp/wet. At the moment it is quite cold here (around 1-2 degrees celsius), maybe thats why.

I havnt encountered any issues with reusing my shorts, I do however use a clean pair each day. So I would say its probably fine.