I have also only been riding for about five years, but I typically get in about 5,000 miles a year now. I just received my Cannondale Evo with DA di2 and I have only ridden it the past two weekends. Also, my mileage has been limited to about 40 miles per weekend since I just started riding again due to suffering a broken ankle back in October. Regardless, here are my comments about di2 vs a six year old Look 555 with Ultegra.
* A lot of guys have posted about the elegance, simplicity, and connectivity of riding a mechanical gruppo. I get that, completely. Someone mentioned Ferraris with manual trannies. I was also lucky enough to have a Ferrari with a six speed and would never have a car with the F1 paddle shifting. I test drove a first generation F1 tranny in a 360 Modena, didn't like it at all. You can't blip the throttle between shifts, no interplay between the clutch, brake, shifter, and gas pedal that required some coordination, etc. This is actually a reasonably good parallel to the mechanical vs. electronic shifting debate going on here. However, unlike the 6-speed vs. F1 options on the Ferrari, the di2 is growing on me.
* Some of the things my Ultegra gruppo did tipped me off about things. When I hit the bottom of a hill and started downshifting, the FD would start ticking on the chain if I got down to the second or third cog without getting off of the big chainring. Maybe that should have been adjusted away, but I kind of liked it. Same thing when I was going downhill and moved out on the cassette, the FD would politely let me know when I got way out there on the cassette. Without that, I find myself cross chaining more with the di2 because the FD autotrims out of the way and takes away my auditory cues if I have been inattentive.
* Since the Evo has an 11/25 11-speed cassette and the Ultegra has an 11/28 10-speed, moving from the big to the small chainring means three cogs change up or down to keep the same cadence. On my Ultegra bike, it was two cogs and it simply required a full sweep of the lever when going from the small to the big ring or two quick clicks going the other way. Simple, quick, no precision needed. Just swing the whole lever full travel without thought. Di2 requires a bit more effort, for right now. Since there is a three cog difference, you hold down the button for about 2 seconds, but it keeps going if you don't lift. I am planning to check into reprogramming the di2 so that it automatically jumps three cogs and stops when I hold it down. I practically never need to jump more cogs than that at once. After I do that, I think I will like it more.
* Since I am still getting used to the di2, the tactile feel of the levers still feels just a little bit strange to my fingers. For Ultegra, as mentioned above, getting on the big chainring or downshifting the RD simply required your fingers to sweep the entire handle assembly. You didn't need to find a button. Di2 requires that you find the big button (or small) and press it. Now, Shimano have done a great job of providing an easy way to differentiate between the two buttons, don't get me wrong. I can even feel the difference with full fingered gloves on. I do wonder if I will still be able to do that when my fingers are numb, though. That being said, I have mishifted the Ultegra due to numbness before.
* I find it easier to shift up and down while in the drops with di2. This is because I can simply reach up to the appropriate lever with one finger and 'click', I have my new gear. Don't have to move my hands, just a finger. Maybe my Ultegra shifters weren't well adjusted for my smallish hands, but shifting in the drops required a lot more movement of my wrist and elbow joints to swing the lever through its travel. Once the weather warms up, I expect I will really like the di2 with regular cycling gloves since my fingertips will be resting right on the levers and the difference in the big and small buttons will be much more obvious.
* I can also understand those that don't like the battery hanging off of the frame. Aesthetically, not optimal, but not completely objectionable either. Nevertheless, for me, that's why I went with the DA di2 on my bike. Came with the seat post battery. Also liked the paint job for that particular Evo as well. Hey, you gotta' love your bike, right?
* This isn't so much a mechanical/electronic issue, but guys that live in hilly or mountainous areas will appreciate the 11-speed cassette on the new 90xx DA gruppos. The 11/25 11-speed really provides a nice gear selection that allows you to nail your desired cadence on the climbs.
* A couple of people talked about the electronic gruppo being heavier. Not really. The 9070 is slightly lighter than the 9000. However, I haven't seen any writeups, articles, or statements from Shimano to indicate if that comparison includes the battery . Regardless, my 52cm Evo came out of the box at 13.6 lbs. or so and 14.0 with some older Look (non-carbon) standard pedals. I have the compact chainrings installed and they sent it with 170 cranks. That weight includes the battery. My Look 555/Ultegra tips the scales at 18.8 lbs, although it has Mavic Cosmic Carbone SL wheels with a Powertap hub accounting for about 2 lbs. of the difference.
* When shifting, the FD can be heard. The little micromotor in there sounds a little like some sort of motorized gizmo from a science fiction movie. I suspect the riders in the immediate area can hear it too. That could bother some people, I suppose.
* As far as maintenance is concerned, the di2 is, maybe, a little trickier to initially set up than a mechanical group because most shops are simply more skilled working with mechanical system. I haven't had the di2 long enough to speak to the ongoing maintenance requirements, but I will say that I generally expected to replace the cables on my Ultegra bike about every two years or so if I wanted the shifting to stay nice and crisp. During that time, I'd usually have to give the barrel adjusters a quarter turn every once in a while as the cables stretched. Will not have to do that on the di2 bike.
All in all, I think that I will grow to like and probably prefer the electronic shifting option. Do you need it? No, not at all. Will it make my rides more enjoyable? I dunno'. Maybe, after a while. I can see why a lot of people like it already. I may have more insight after a couple of months and I do a ride on my Ultegra bike. I am sure the di2 'advantage', if there is one, will jump out at me then.
2006 Look 555 Ultegra
2006 Felt B2 Dura Ace
2013 Cannondale Evo HiMod Dura Ace di2