Higher resolution is need when developing, CAD (and probably in all media creation apps), in general when you have lots of toolbars, toolboxes, and a content window in center
Spaces won't solve the problem when you have one application that needs lots of pixels... but it would still be great to divide all your open apps into categories
I've had 1920x1200 on different 15" since 2003, though I've had 1600x1200 since 2000 (the standard aspect ratio of the wide 1920x1200). And I wouldn't say that it has affected my vision any more than age has in itself. what has from time to time affected it is doing 16hrs workdays staring at the screen.
You really need a good screen though, I had a Dell (Latitude 810?) with a really unsharp screen and then it was a pain on the eyes, now with HP NW8240 with a really sharp screen it hasn't been any problems.
A couple of years from 40, I will probably take the step up to 17". What has been holding me back from MBP with Bootcamp is the crappy resolution, but now I can get a MBP for my heart & soul, and the resolution I need for my work in the windows world