It really is true that geography plays a huge role in all of this. I live in Canada, in Ontario, in a small city that pretty much revolves around the university. My husband's an academic, and until recently, I taught at the university as well. Before that I spent a LONG time at a much bigger urban university. But again - Canada.
What I've noticed is that at the bigger urban university the dress code skewed towards British frump (British friends, please excuse me, I do not mean fab British style!) whereas in my current town the code skews to boho, with many late-60s hires and fashion holdovers. That is why, wearing a relatively fitted cotton dress and patent leather sandals, I would stand out at a function as very dressed up.
I tend to like to be on the "dressy" side for my environment as well, but there's a line I wouldn't want to cross at a function like this because one can risk making others uncomfortable. If I wouldn't feel physically comfortable in an outfit, if I felt too "uptight" or too exposed, or too blingy, I wouldn't wear it. But then I wouldn't want to wear an outfit like that in ANY environment, so maybe that's just my personal preferences talking!
I definitely second the argument NOT to wear high stiletto heels. A wedge is totally fine, but a heel that will dig into floors or the garden would not be very comfortable.
ETA: would agree wholeheartedly with Gaylene's comments re the big donor in cowboy boots, etc. That sounds totally Alberta to me. Not sure if the US mountain towns are similar in tone.