I just upgraded from the IP4 on ATT to the IP5 on VZ. If I were you, having seen the rumors popping up about the 5S I would wait.
The IP5 is a huge step forward in hardware performance period. It is faster and apps run much better on it. Also you get LTE.
The new larger screen is a nice to have as far as I am concerned - both are retina.
It is much lighter and I like that the back is no longer all glass.
Software you get Siri, panoramic photos and voice turn by turn directions in the IOS software on the 5 and NOT the 4. The caveat to that is I find Siri is a nice to have but not necessity as there is already dictation on the 4. Panoramic photos are cool but not a reason for upgrading hardware. And you get a much better map app with Google Maps for FREE with Voice turn by turn directions on the 4.
I personally don't have regrets upgrading as I needed to do it to take advantage of the Share Everything plan with my wife and her 22% discount through her work.
If you think you can continue to live without LTE and don't absolutely need the new features in hardware and software in IOS6 then I would definitely wait for a few more months for the 5S. If the rumors are true and the 5S comes out in June and has all the new options in colors, screen size and new hardware you may be better waiting 6 months AND you can still sell your 4 for decent money. Like I said, if I wasn't making the switch from ATT to VZ to take advantage of the discount I would have waited it out for the 5S.
BTW - giving them your 4 for $110 is highway robbery. It is convenient for you but right now if it is factory unlocked you can get $250-300 on CL or Ebay. You can at least get $150-180 on gazelle.