For me, first is aerodynamics, so adding bullhorns with TT or Microshifters would be great if I could get the handles in the right position to be able to put as much power down. The Di2 satellite shifters would be a tad more aero and if they are possible without brifters then I would go that route if I didn't have to pay retail. I don't mind paying for good stuff, but if I can get a good set for about half of retail then I'd be all over it in a heartbeat.
Wheels, currently I have a new 35mm Scirocco front and 50mm Bullet back, which I plan on going 50mm Bullet front and disc in the back. The bike is set up as a rim brake now and will likely stay that way because going back to disc brakes would require a huge chunk of change for DB wheels in a similar depth and new hydraulic brakes.
Now it is set up as a 3X10 Shimano 105 (11/28), but I plan on going to a 2X10 (53/39) with 172.5 or 175 cranks, and an 11/25. For some reason I like longer cranks, at least on a DF bike, but I have only tried 170 so far on the V20.
I hear what you are saying about electronics. I like being able to work on my bike on the road if something happens, so mechanical is best. More precise and faster shifting is great for shaving a few seconds here and there. But at what cost? a lighter wallet and the possibility of being stuck in 1 gear all the way home hahaha. Like you, I want to save money in the process if possible.