OK, apart better fuel consumption, what's the big deal for the Gen4 Prius?

I own a Gen3 Prius since Sep. 2009 (with about 95.000km). I am really in love with the car, its driving and the HSD.
The fuel consumption on average is very good, considering my driving style, where I mostly drive (city traffic on hilly terrain) and non-flat region where I live.
I really really like the Gen4. I like the design, I like the updates, I like the looks. I really feel I want to upgrade.
But then....
Then you start looking at the numbers, at the €€€€ and you think - is it really worth it?
Why should I sell a really good Gen3 that so far had only brake pads and discs changed (salt used on the streets here in winters and you don't use brakes enough to clean them from forming rust), and a couple of lamps, and gave me so far no other trouble? Sell/replace a car that essentially looks and feels new?
I have tried to estimate the fuel savings with a Gen4 vs Gen3 based on my current statistics of average fuel consumption, average fuel price and I ended up with a net saving of 1800€ over 6 years... that is 300€ saved in fuel per year. I hardly recover any fix costs, let alone purchase price...
So I am wondering and I ask to those fortunate here that have had already or will have soon the possibility to drive the new Gen4, what else is *really* good compared to the 3? what makes it really *worth* moving to a Gen4, considering that, even if I get 10k€ back (official estimate on my Gen3) from my current one, I need to dish out at least another 15k€ to buy a new one?
Yes, maybe I could lease it with 0€ down-payment, with 500k€ monthly payments (and ending up after 3 years and 18k€ later, with no car in my hands).
So - what to do?
(the Prius Gen4 will be launched in Germany end of January, no official pricing, fuel consumption estimates (for what the EU ones currently are worth, I refer to the EPA ones - which are really meaningful), so all the above is based on the current prices of the Gen3, which I hope will be the same, or higher (!) than the Gen4 )

 

I have just found out that the Reverse still plays a useless and annoying beep *inside* the vehicle when engaged:

Let's just hope that you can turn that off at the dealer's. Because this is the most nonsense thing ever. And if you have rear parking sensors that beep too, you can literally go insane...

Thanks BTW for all your replies. I think I need to wait for the Germany pricing to come out, test drive it and then see what the dealer in Germany wants to offer me. I cannot lease the car because I am not a company or a professional. And financing it at 3% interest might not be the best solution, as it also requires me to get a more expensive Full-Kasko (I don't know what it is called in the USA) insurance.
The business case is extremely thin so far. And as I said, fuel savings alone don't bring much at all compared to my Gen3.

I know that Toyota has stated they are expecting to sell the same cars as last year, and they have reduced the outlook of Prius sold worldwide due to lower gas prices. So, if they want to see more Prius sold and the dealer doesn't show me he really wants to sell it, considering I don't really need a new car right now, I think I will stick to my Gen3 and see what happens in the overall Toyota line up. (e.g. like a new Auris, which is cheaper (and smaller) but currently offers a behind the wheel instrument cluster and no HUD, which for me are total deal breakers - in city traffic where I mostly drive, I need to see in front of me at all times - the Prius in this respect has helped me save a lot of possible accidents due to "Facebook Drivers" who don't really pay attention while driving.