I will also add a very resounding Yes to the chorus.

In my monthly TG support group not too long ago, I met someone who came in after a long day's work. Her makeup was running quite badly due to the heat, to the point of distinctly uncovering some beard shadow. I really really felt for her.

Fast forward a few weeks after that, I was driving up to meet my gatekeeper psychiatrist in another city (it's a 3-4 hour drive each way) and it was a scorching hot day - about two hours in, I realized that I was starting to sweat rather profusely. Visions of having my makeup running all over the place flashed through my mind. Fortunately, through good quality cosmetics and judicious aiming of the air-conditioning vents, I managed to keep everything together for the entire day without touch-ups or reapplications. So, long story short, yes, it's worth it!

I use MAC cosmetics but I am looking for cheaper alternatives for everyday use. Like Buffy, first I clean my face - among other things, this prevents the sponges and cosmetics from getting contaminated by bacteria from the face. Then I apply either an oil-free moisturizer or a moisturizing non-comedogenic sunscreen, followed by foundation, concealer, blush and powder. I usually apply as little as possible, ensuring that I blend the foundation into the jawline to prevent the mask-line appearance.
Oh, having the shade of the foundation accurately match your skintone is important too. Unfortunately, this definitely requires the help of someone from the cosmetics counter.
Hope that helps, and have fun at the ball!
Claire