I also suspect the survival ratio of paperbacks is 10-100x the survival rate of comics, because as you say adults bought them. (Although I'm sure kids also bought pulps and paperbacks, they were not the primary market for them.) So, even if they were viewed as more disposable than, say, hardbacks, they were much less likely to be abused or casually dumped. If I wanted a copy of Ace Double D-15 in a hurry, I could get one today for under $500; and it's a strong candidate for the most desirable Paperback out there.
Pulps, I think, are soft in the marketplace right now because a lot of collections are turning up as the collectors pass away. I've seen more pulps the past decade than I ever did the 20 years previously. Pulps also seem to have survived the paper drives far better than comics; just based on what I see show up it seems people started seriously collecting them in the late 30's- early 40's, and issues from that time forward are fairly easy to locate for the most part. (As always, there are notable exceptions.)