I'd guess that if anything they'd increase the pressure to raise the boiling point. That way things dissolve in it faster and the water doesn't evaporate away.
Part of the flavor of maple syrup is due to caramelization and the Maillard reaction of components of the sap. Just concentrating the sap would get you a syrupy substance sourced from a maple tree but it wouldn't be maple syrup.
I've never liked the flavour of maple syrup very much. At the same maple syrup place visit, we had some, on pancakes. WTF? This is plain table sugar! What kind of stunt are you pulling here? The guy supervising the boil said don't you know? The very best grade is like that, hardly maple-y at all! Turns out it really was about the sugar all along, with the initially undesirable maple flavour coming to be prized over time as a side effect.
Fun fact, early abolitionists marketed maple sugar as a replacement for cane sugar, since cane sugar was made by slaves while maple sugar was made by northern farmers.
So the old grading system rated the lighter colored plainer sugars and syrups higher than the darker more flavourful varieties. Since less maple flavour made for a better all-purpose sweetener and a more direct competitor to cane sugar.
Nowadays we usually use maple syrup for the flavour, so the grading system is non-judgemental that way. And the darker grades are more likely what you want.
The stronger colors and flavors occur later in the season. The warmer weather allows more bacteria growth in the sap, which metabolizes some of the sugar into other compounds.
