I'm prepared to be shot down in flames, so fire away!
No by me. I don't really care, but there has been a lot of discussion on the forum of the last year why your approach is not a good idea. As long as you can control the level of noise on that unused pin, your approach works. Moving a hand or anything else near that pin changes the value that analogRead returns - sometimes to very consistent, repeatable values. Then, there goes your randomness.