I'll add my two cents to this conversation -- a little late, but I didn't know about this thread until today.
Victoria Holt and Phyllis Whitney were the backbone of my reading material from about age 12 or 13 until about my mid-20s. I believe I read every title either one of them ever wrote (except for their last few -- by that time I had started to outgrow them and move on to other things). I also read several Jean Plaidys in my 20s, mostly her books on the Normans and Plantaganets. I think I only read one or two Philippa Carrs -- by the time I discovered that pseudonym I was already losing interest the author.
Over the last couple of years -- after a hiatus of 20 or so years -- I decided to give them each a try, again. I've tried one or two titles by each and, alas, none of them have held up well for me. I now find Plaidy/Holt/Carr's style of dialogue waaaay too stilted and emotionally flat -- I suppose one could argue that it works in conjunction with her books' typically Victorian settings, but I find it unappealing as well as too predictable (if you've read one Holt heroine, you've basically read them all). Phyllis Whitney's style of characterization and dialogue held up much better and, surprisingly, the two books I tried didn't feel dated. However, her method of creating suspense is way too heavy-handed and melodramatic.
So -- I will always have a nostalgic fondness for Plaidy, Holt and Whitney as the authors I cut my teeth on, but their books will remain in the attic, so to speak.