Celebrities have always visited the show and presented prizes in some fashion.
Yeah, you could call Janice, Dian and Holly celebrities, sure.
That's not entirely fair...celebrity walk-ons and prize presentations happened in the Barker era, too. They're just happening more frequently now.
I'm curious as to why fans dislike the guest appearances so much. Some are more enjoyable than others, sure, but even if they aren't, I don't think it takes anything away from the show as a whole.