I faced the same dilemma since I’ve acquired many of the Paraliminals over the years. There were several reasons I decided to invest in the CDs.
1) The CDs should have less background noise than the tapes. This wasn’t a huge consideration because the tapes are so well made.
2) The sleep learning track sounds like a benefit that I can use.
3) The used tapes can always be sold on e-bay, or given away as gifts. When I think about it the idea of giving a tape to a friend who is struggling is a gift for both of us. How often do you have the opportunity to make a profound change in the life of someone you care about? I know I’ve given the tapes as gifts before, but many times I’ve thought about giving one and have never gotten around to ordering a copy. Having some extra tapes on hand seems perfect.