The only reasons to update are
Technology is too old (looking at A8 *.*)
Technology is no longer supported by the company's support system.
Technology has features you truly need.

I like many programs, but If I did yearly updates, I'd be broke. I have to earn enough to justify an upgrade and the new features have to justify the upgrade. Back when 3ds max published and upgrade every year, I never upgraded yearly. $3000+ I would need to earn 4 to 6 times the cost to justify the upgrade. However, as I am new to Unity jumping in here is the only real option.
@nuclear_winter if you can earn more with Unity 4.x then do.. Until your earned pay or feature absolute need justifies the upgrade. I am sure you can produce CandyCrush 20-50 with it and earn tons. i.e. It's still viable and indie developers earn on the strength of their creation not on cutting edge feature.
Maybe I am talking out of place; however, The current top indie games(1-4) probably can be made without an upgrade and their earnings will justify the upgrade. If the hobby is to be on the cutting edge of game tech, than you'll have one very expensive hobby.