Cassette tapes "won" market share over most of the other analog audio formats, because they were durable and convenient, not because they had the best sound quality. However, cassette tapes, and all analog audio formats, have now "lost" to digital recording, because of the quality of digital, and the preservation of quality when making copies.
All cassette tapes wear over time. While fairly durable, every time a cassette is played, there is an imperceptible loss of quality. With sufficient playback, the loss becomes perceptible. Every copy process also loses quality. Even if you keep a master copy just to make 2nd-generation copies from, you have to play the master copy to make the 2nd-generation copies, so early 2nd-generation copies have better quality than later 2nd-generation copies.
I have digitized all of my audio collection, and now have them on CDs, and on the hard disk of my computer. I no longer have a tape player in either of my vehicles. I don't expect to ever again purchase a recording on cassette tape.
I highly recommend that anyone still using cassette tapes strongly consider the purchase of a CD player. If you have a computer, you already have a CD player... just hook up some decent speakers, or trail a wire to line-in on whatever other sound system you have. CD players can be obtained for your car for as low as $50 at WalMart.com, or $120 for one that can play MP3 format. For your home, you can obtain a boombox type CD player for as low as $20 at WalMart, or $30 for one that can play MP3 format. Naturally, you can spend more, and higher-priced systems may offer better sound quality. If you already have a quality sound system, you can get a player only (no speakers) to hook into your existing system.