I strongly considered buying a 730 (or 830) as a replacement for my Lumia 620. But comparing with the 925 for only 230€:
8mp > 6,6 mp, S4 1,5Ghz > S400, Adreno 225 > 305, 4,5" > 4,7" (for me), hardware navigation keys.
Yet, the Lumia 925/920 is 2 years old and battery life on the 730 is probably much better. But still, I'm not sure whether the 730 is really the best option as a replacement or not.