Congratulations! You just saved a cassette recording from an analog demise. Since you have a WAV backup on disc, you can delete the WAV files from your computer now if you wish.
Before you do, though, consider sharing them with the world on sites like Archive.org or SoundCloud. For my high school garage band's demo tape, I posted the tracks on SoundCloud
along with a shot of the original artwork. From there I can share it with all of my friends and hold onto the hope that someday my own kid will dig it up and give it a listen.
I hope you liked this tutorial on converting tapes into MP3s. To see a video version, head over to CNET How To