Is system synergy worth having matched components?

Synergy,yes! It is important.

Same brand, not really. The pair from same brand is the understanding of the designer. The pair could be good one, but not great one. You might found the great match on the market with different brand.

Just like me,

I found Rega cursa 3 + audio research vt100 iii is such a great match.

I also found Ayre kx-5 + audio research ref 75 se is very good.

It is the journey, believe me. Everyone explore the hifi world, including the designer.

No one can set the superior standard, as there are more great match who they do not know even they design.

How would we know if synergy can happen?
Or is it the we get every preamp to go a specific amp or visa versa?

On the amp to speaker side, it is pretty clear that a small SET running low sensitivity and.or low impedance speaker is going to not really work.

What is the process that a person using a “synergy based” approach uses to find their gear?

I wonder about that too. I think that's what reviewers refer to as "the loom" - staying with the same brand throughout, particularly with cables. Please correct me if I got that wrong. My current system sounds great but I often wonder "what if I tried "X"? That will be a very expensive route with no promise of improvement.  Recently I purchased Synergistic's Foundation silver XLR intertconnects and their atmosphere 2 digital cable. Sounds great. Today there was   an Audiogon ad for an top of the line Audioquest WEL signature XLR cable for $1,500.  I wondered - Hmmm. Then I told myself, stop doing that  - you're listening to the equipment, not the music.

Often the truth is some manufacturers "add" other components to their lines for a brand and sales benefit, when their core skillset or best product is one particular type of component.  

Nothing in my system is brand matched, and I would have it no other way. 

I have always mix and matched brands up until I fell in love with Pass gear XP30 Preamp X350 Power amp the synergy is just outrageous I will never go back to mix matching.  @jasonbourn52 you nailed it drove it straight home. as stated above  someone can`t hear worth a damn  I totally agree what profound statement. I`ll bet you there system is something I would`nt want to listen to.