Do high dollar mono blocks truly improve the Sound Quality over the mid tier amps

I would consider eliminating the preamp as you have the MSB reference Dac. I would also recommend trying a pair of MSB m205 monos. I went from D’Agostino momentum m400 with momentum pre and a discrete Dac to a premier and s200 and am loving it. The pairing of the MSB amp and Dac is great. I will soon upgrade to either the ref or add the digital director.

Great great room  

That’s a lot of glass. Curtains? Other treatments as tolerated. 
 
Pre Amp

Streamer. (Grimm MU2?)

Re original query:  In general, yes.  Price will vary by intent or depth of pockets...

I see "zero" acoustic treatment in a room which appears to be very lively with lots of hard, reflective surfaces. You may not even know how good your system can sound presently. I'd suggest starting there before spending another penny on equipment.

The OP is asking if higher end monos "could" be a significant sonic upgrade.

IMO absolutely yes is the only answer, but the real question is how much is the OP prepared to spend, because price is MORE OFTEN THAN NOT an indication of ultimate quality.

Example: the difference in sonic quality and price between the Deltas and the new 7 series from Soulution is vast.

One way to be sure of the pairing is to ask Wilson which amps they use when they display/demo at Munich and/or Axpona. They'd know better than anyone here how to get synergy with their speakers.