Is the NIDNTTE worth the money, if you already own the 'old' NIDNTT?
Have you read the description of what's new on this page? http://academic.logos.com/2014/09/17/the-new-international-dictionary-of-the-new-testament-theology-and-exegesis-a-wonderful-new-edition-for-new-and-devoted-readers/
I took a long hard look at buying the upgrade. In the end, I decided against it. The Greek Literature section seems helpful. But I got the impression (after comparing the new to the old article on Abraham) that instead of editing the articles for the sake of clarity, Silva also edited them to conform to a (more extreme) conservative evangelical perspective. I could be wrong, though, since I could find just the one long article with which to do a comparison.