I have spend lots of time and money to dig up Carla Kelly's Signet Historicals, just because I really like her style in the books released by Harlequin in the last few years. I just recently found a blog by her (called Random Natterings) and found the following amazing information:

Through the years, I have noticed with some amusement and amazement that the used book prices for my early Signet works ... have shot through the roof. By their nature, paperbacks have a relatively short shelf life. I've been told by many folks that they hang onto my paperbacks and don't trade them in. This means some of the books are somewhat hard to find...
This has meant some amazing prices. A new copy of Regenecy Valentine II (ever heard of it?) goes for a whopping $347.13. That hardback of Daughter of Fortune (my first novel) commands a $159 price tag. The Lady's Companion sells for $53.70 used. Summer Campaign, my first regency novel, sells for $89.95.You get the drift.
Fast forward to ebooks, principally Kindle. Cedar Fort already has ebook privileges on Marian's Christmas Wish (out now). Also in the ebook works through Cedar Fort are Reforming Lord Ragsdale, Summer Campaign, and Mrs. Drew Plays Her Hand. To start, some will be issued only as ebooks, and if the demand is there, later as softcovers. "Marian" and "Mrs. Drew" (next Christmas, folks), will be in softcover and ebook. Currently there is also a 4-novella collection of my Christmas stories available through Cedar Fort only as ebooks.

Libby's London Merchant and One Good Turn, because the latter is a sequel to the former, will be reissued by Signet.

If you see these books coming back into print or as eBooks, the value of the old ones is going to drop like a rock! Ebay, anyone? Remember the hard-to-find Tall, Dark & Dangerous series by Suzanne Brockman who have all been reissued? Just a warning, in case you wanted to leave those valuable books as an inheritance for your kids...   On the other hand, I really enjoy Carla's historicals for their emotions, their not-usual (not of the ton) but wonderfully strong and curageous heroes and heroines, and the pictures they paint of that time.

I can't believe people pay those prices for used paperbacks!  I'd love to get my hands on the very early Diana Palmer books but I refuse to pay outrageous prices for them.

I sold off all of my early Jennifer Crusie books before they were all reissed once they started going that way.  I'd discovered her early on in the Loveswept line and bought her stuff then.  Once they started getting reprinted when she went big, I Ebayed what I had left, figuring I could repurchase them later if I wanted too.  Only one I hung onto was Sizzle, a short novella that I doubt will ever be reissued.