My anime soundtrack selection stands at about 40 CDs...
small in comparrison to my Anime and Manga collection, but ever growing ^^
There not a waste, not if you like Anime music their not. Like with anything you got your bad OSTs and good ones. Anything Yoko Kanno is always a worthy buy. Ghost in the Shell Sac, Arjuna, Escaflowne... etc. I usually only buy the soundtrack from a series I've seen, that way I know if I like the music or not. I also like listening to Anime OSTs because I like instrumental music, and listening to it helps me wind down at night and sleep.
Like with any form of commercially released music... it's really all comes down to personal taste.