I flip through a lot of LP's in a lot of thrift stores and during the past year or so I've noticed the number of people browsing cassettes has gone up quit a bit. Some of those stores had no cassettes for a long time but they're back on the shelves again.
Where I live, lots of used cassettes - pre-recorded and good quality home-recorded - are available at thrift stores, but don't get picked. Vinyl is popular, however. I snag plenty of tapes and some of those are typically large drop-offs from the previous owner. I gave away a lot of my pre-recorded tapes years ago, and now I find myself picking up used ones, but mostly titles I don't have in any other format.