Yes, I know others were wearing sunglasses (I can't believe I'm talking about this...). I don't think there's anything inappropriate about wearing sunglasses when you're sitting in the sun and wind for three hours.
But, a smaller, less dramatic frame would have been, IMHO, a better choice for the occasion.
(Still friends??)
Personally it does not bother me either way I used to wear contacts and I would have needed sunglasses in that bright sun. Also somepoeple need large lens ones because they have a lot of peripheral vision and smaller ones are not effective because the light is still visable.