Up to about 150dpi, I'd prefer just using the resolution for more 'space'. Certainly on a 30" monitor, I think 4K resolution would look fine without the DPI scaling. I'm writing this reply from a Vaio P-series with an 8" 1600x768 screen, and again I don't use DPI scaling on this one either, however I'm also about half the distance from the screen than I would be on my desktop monitor.
Most new programs seem to scale reasonably well. But windows strong point was always backwards compatibility. A lot of old stuff does still work in Vista / 7 but doesn't really deal with scaling properly. I think if people started buying higher res screens, application developers would fix the remaining problems.