In my experience---wheels are a noticeable upgrade (as you noticed.) Beyond that, not so much. Almost all the benefit is the all-important placebo gain. If you are running 105 or above (or whatever the Campy or SRAM equivalent) then nothing you change is going to do much besides lightening your wallet.

The Most important thing is a comfortable bike. If you don't like riding you won't ride. if you are strained and contorted or overstretched, you can't make a big effort or ride a long distance. If you really like your bike, you have achieved Bike Nirvana. Anything beyond replacing for wear is money wasted.

I speak as one who has wasted a ton of money and actually learned the expensive lesson. Now my bikes are just "my bikes, which I ride" not projects, and having "the latest" doesn't interest me. It never gave reward commensurate with the cost.

Eventually you will be able to afford a nice aero disc bike ... and you will find that there is a six-percent increase in speed (detectable by computer only) and a slight increase in road vibration. The vibration is constant, the speed gains come only when you are riding fast. At lower speeds (sub 18 mph or so) the gains are so marginal as to be undetectable.

However, the new bike will have all the latest stuff, and it will be new and cool and fun and worth it.but if it doesn't happen for three years or more .... that new bike will just keep getting better, while your appreciation of the Boardman will just keep growing. Win/win.