Using RealMedia as a positive example gives me goosebumps, but I'll use them anyway. It's too late for the initial boxed version, but once the next 20,000 copies are needed, and for the downloadable version...
I really think the Aquarium should prompt users once a month "There may be a newer version of the Aquarium with more fish, a new background and coral, specialty creatures, and other exciting features. Many of these upgrades will be FREE. Do you want to check?" [Yes] [No] with a little checkbox at the bottom "[X] Don't show this again for 3 months."
I did campaign for all 7 fish slots being set to RANDOM automatically in 1.0 and 1.1 and won.

I wish I'd thought of this and pushed the idea earlier. I didn't realize none of the printed materials the Aquarium comes in would mention free upgrades to the things I suggested above.
I know Prolific wants to legally protect themselves from promising too much, but I think they hedged a little too far by not mentioning upgrades anywhere.