Today I wore one of my favorite shirts to work. It's comfortable, the color is good for my skin tone, and the cut flatters my figure. But I won't be packing it for RWA.
Why not? Two reasons: 1) The back wrinkles like an accordion from the simple act of sitting in a chair all day, and 2) if I sweat the tiniest bit, it shows.
Which brings me to an important conference-dressing point. If at all possible, buy any new clothes you need well before the conference and wear them a time or two. Barring unfortunate tomato sauce accidents, they'll still look new, but you'll know if they tend to wrinkle or show sweat or the middle button pops loose every time your purse strap so much as brushes it.
I plan to follow my advice for everything but my awards banquet and publisher party dresses. I have so few dressy occasions in my everyday life that I neither own appropriate dresses already nor have any reason to dress up between now and then. But everything else gets test-driven.