Future risk of computer farms generating addresses for previous balance?
I think the way to reason about this is to think about the incentives and rewards of such actions.

Yes, I can potentially throw a lot of computational work into generating private keys and checking their balance... But is it really worth it knowing that I can throw the same amount of energy into Mining, and get a guaranteed and constant return on my computational work?

Somebody was discussing something similar in 2012 on BitcoinTalk, here's the link https://bitcointalk.org/index.php?topic=107172.0. Note that the author of the post says that "you probably have much better odds finding extraterrestrial life or winning the Powerball 5 times in a row" than randomly finding a generated BTC address with a balance in it.

EDIT: Reason for the downvotes? Why did a couple of people damage my account reputation without explaining exactly what is wrong with my answer? So sad this community is not as nice and newbie-friendly as it should be.