Buffy the Vampire Slayer is a good example of them not sexing up the female lead, yes SMG was/is a very attractive woman but they never made a big deal of that as GW has always had strong female leads in all his projects.
and as for toning down a female leads sex appeal they tried that with the naturally blond Gillian Anderson in the X files, that backfired and they made her a total sex symbol to a Very large part of that shows viewership