Hey, ignore the realist! I think it sounds like good clean fun!
Either for now or later, ideas are; (1) Noise decibel indicator (2) Speech, radio shack has a 10 (or 30?) second recording module for $9.95 which records with one button then plays that back with another button as often as wanted. Small, circuit board, no case, but everything else. Just for like say "Computer on" or "Scanning" or something. (3) Altitude indicator can be more fun than you think. (4) Ultrasonic range detector with laser designator (down to about $20 now for a 1 to 40 foot model). (5) Non-contact distance surface temperature thermometer, unless one of those you mentioned does it, about $80 to $100.
Have fun, HobbyBot
PS I would like to see this thing when finished. email@example.com