The Haleakala volcano is the most beautiful pain in the butt you'll ever encounter (unless you run into Naomi Campbell on a bad day). You drive two hours up a winding road with occasional guard rails to 10k feet only to experience bitter cold, relentless winds, and unpredictable weather. The fact that you just left the glorious warmth of the Maui beaches makes the experience all the more harsh. In spite of the difficulty, I can wholeheartedly say that our trip to the summit of Haleakala was one of the highlights of our stay in Maui.
My tip to maximize the fun and minimize the pain?
Skip sunrise and take in the sunset! Everyone talks about sunrise on Haleakala. It's (in)famous, and tourists get up at 3am (!!!), drive up a mountain in the dark, fight through crowds, and don protective gear just to experience the first rays of light peeking over the caldera. While I have no doubt that sunrise is beautiful, sunset is also stunning and offers several advantages.
1) Sleep ~ Unless you've just arrived and are still on mainland time, a 3am wake-up on vacation is probably not your idea of a good time. By going at sunset you can have lunch, enjoy the afternoon in Kula, and still arrive in plenty of time.
2) Traffic ~ Since the crowds want to see the famous Haleakala sunrise, the two lane road is often backed up all the way down the mountain. Some people never make it to the top and get to enjoy the sunrise over the switchbacks in bumper to bumper traffic. Definitely not worth getting up early for.
3) Parking ~ Even if you make it to the summit in time for sunrise, you will need a place to put your car. The lots fill up early, especially at the prime lookout points. In contrast, on the day we visited at sunset, the main lot was less than half full.
4) Warmth ~ By no means is sunset on Haleakala warm, but standing outside during the last warmth of the day sure beats standing out during the coldest part of the night. By the time the temperature starts to drop, you will be back in the car with the heater cranked up, heading down to dinner. Regardless of when you go, plan to bring long pants, closed toed shoes, and a jacket, preferably with a hood. Some hotels have blankets they will loan you as well. This isn't paranoia. With temps 30 degrees below the beach communities and winds up to 40mph, you will need all the layers you can get.
5) Wind ~ The wind generally comes from the east at the summit. This means those wanting to view the sunrise must face into the wind, while those there for sunset have the wind at their back.
Good luck if you choose to go! I hope you are rewarded with conditions as wonderful as we enjoyed and a view as beautiful as this: