Yes. You can still sell prints of uncopyrighted stuff.
Your software argument is even better evidence that 20 years is a good idea. If the software is maintained, the new, derivative versions continue to be copyright protected. At the same time, abandonware becomes available for use without worry.
Here's another thought experiment. Assume Spiderman was first created in 2002 with the launch of the movie. It would be expiring soon. They've already made massive profits and such old movies are found for bargain-basement prices all over, so there's not a ton of money left to be made.
What does Disney have to lose? Just the idea of Spiderman himself, but would you rather see Marvel's spiderman or Warner Bros making yet another failed superhero movie? The latest Spiderman movie would still be available under copyright for another 20 years too. The only way Disney loses is if Warner Bros actually manages to make better content than disney makes. If better content COULD be made, but is stopped by copyright, this runs counter to the copyright's purpose according to the US Constitution.
Summed up, long copyright only serves to lock-in big companies and protect them from people who could do a better job with the ideas than they could. Everyone is worse off except the company's stockholders.