upgrade Dynaudio Special 40 to Kef Reference 1

In this particular case, I am going to speculate that personal preference will be a big factor to determine which one might choose.

I owned Dynaudio Monitors and now own similar KEF though not these two specific models. They are two very good but very different sounding speakers.

I find I do prefer the more coherent sound of the KEFs especially if not listening from more of a distance. I tend to like coherent source designs in general.

There is no upgrade! These are expensive speakers! For this kind of money they should be perfect! Are we talking about the audio hobby here? Foolish statements!
Both of these speakers are fairly cheap in the scheme of things. A $50k speaker will be classified as an expensive speaker. The Wilson $800k speaker is a more expensive speaker.A perfect speaker? No speaker is perfect, not even the $800k Wilson. 
There are upgrades in this hobby, not necessarily based only on amount of money spent and only the listener can determine if a different speaker is an upgrade or sounds better than another.

Yes, it is an upgrade.KEF Ref 1 has more defined treble, mids are more detailed and tones are more accurate, bass goes deeper and has more substantial weight.

That said, it is not necessarily better, as the special 40 is less neutral, produces louder bass and slighlty more elevated 100hz which makes it more "satisfying" to some people. A friend of mine did that exact same upgrade although he has a H190 instead. He finds the Ref 1 to be the superior speaker, but still misses the more "fun" (I can't believe I'm saying this for dynes) special 40.