I too have a 1520 and while I love it, I agree that the phablet lacks the scaling required for its 6" 1080p display.
The phone is great, but apps appear no different than my 1020 or my Sister's 520.
Instead of embracing the larger and higher resolution screen, it seems like Microsoft adjusted the Usability Settings -- settings that magnify the screen and native apps, instead of taking advantage of the additional real estate.
I had hoped that WP 8.1 would work towards making the 1520 more useful, but it's looking like we'll have to look to future updates for any more added capabilities.
BTW, I think this issue is unique to the 6" 1520 and possibly the 1320 only and does not effect the full HD icon/930 with their 5" display.
Unless more manufactures release 6+" Windows Phones and the 1520 wasn't a fluke, we may have to wait a long while or be happy with our (ATT's) decision to back such a niche phone.
That said, its a great phone for grandparents' even if it is a bit costly!