My 2c: those are not exactly paper-thin profiles. Low for an SUV, but not like rubber bands. It's a sidewall of just under 10cm vs 12cm - will it make that big of a difference vs the tradeoff on looks/exclusivity?
Play around with a calculator
https://tiresize.com/comparison/
On the costs: have you actually priced the tyres for current and proposed sizes? There may not be a huge difference in price despite 19 vs 21 inches - my FIL for instance has some strange 18" size on his E-class that is more expensive than the 20" PS4S on my M5.
I get the examples of offroading, but I don't think 19s or 20's or 21s are going to help you much if you should really be in something better suited. Depends on how often your lifestyle demands this sort of functionality... the story of guys buying a bakkie on the basis of 'needing it' for household use vs. paying for delivery the 2 or 3 times in a year you need it. X1/3 etc are not about offroading: rather to move your family around (in my mind anyway) in a way that feels like a car but that lets you lug multiple sets of bikes, kid things and sports gear etc around.
No way I would sell those wheels TBH, but then that is with the lens of how I would be using it I guess LOL