I've no qualms with contestants who have already done reality tv, or found initial fame through reality tv, so long as they've actually had a legitimate showbiz career, especially when the "reality tv" is more talent based than being filmed in your bedroom. So pop stars like Suzanne, Gareth and Shayne who found fame through Popstars, Pop Idol and X Factor respectively are good bookings, but people from Big Brother, who have had no actual career other than being a professional celeb/dieter, should be avoided.
SCD is guilty of a few I'm a Celeb graduates, but they seem to gloss over that and focus on the rest of their careers, while getting the benefit of the tabloid interest it gave them. So long as the person has enough of a career beyond that, it shouldn't matter.
I'm not keen on the WAGs either. SCD seems to have been more guilty of it than DOI, but Elen Rivas was something of a low. The likes of Pamela Stephenson and Heather Mills both have their own careers, and were decent bookings IMO, but neither would have been considered if it weren't for their husbands.