I think Di2 is worth it. For me, here's why:

1. You never ever have to adjust front derailleur trim. With regular Ultegra, you have 3 fd positions among which you shift to trim the two chainrings. Di2 adjusts trim automatically for you. With Di2, you forget that people still have to do that.

2. Once it's set up, you never again have to adjust a derailleur.

3. You never ever have to replace aging / dirty cables. And you never snap a cable on the road.

4. No matter how grungy your derailleurs and cables get, you never miss a shift and shifting never becomes more difficult than the day it is new.

You charge the battery a few times a year -- I charged mine 4 times last year for 7500+ miles and never came close to a dead battery. (I charged my Garmin battery countless times.) Besides the battery charge, Di2 is a no-maintenance product.