I just got the NTG yesterday and read for the first time last night. With the NST I used a MightyBright clip on light and while it worked well, it tended to light up the room to a certain extent. With the glowlight only the screen is illuminated. Although the DW never complained about the MightyBright, I think she likes the NTG better.
So for me, it was worth the upgrade just for that part. But then I'm a gadget hound so I probably would have upgraded anyway. And the contrast while noticeable is not a factor for me and the NTG is perfectly readable.