Heyyo! Little late to the party I guess. Lol
My first Moab trip was from late September-Early October of 2015. Let me start of by saying, the weather is damn-near perfect. The daytime climate is great and the nights are absolutely perfect. The stars are purely addicting. I spent 3-4 hours a night laying on the 80's roof staring up at them. If you haven't spent much time out west, they will blow your mind.
I have not been in June/July/August, however a few of the Techs I worked with in Golden, CO were big wheelers. One guy in specific was obsessed with Moab, and made trips 4 + times a year for over 20 years. He "practically raised his kids in Moab". Given, a 5 hour drive versus 25+ makes a huge difference in how choosy you are about dates to visit, even if it is heaven on earth. - Point of sharing this: He told me if I ever planned a Moab trip after mid June, or before late September; to expect to be miserable.
I spent a week in Moab at the end of March this year. Climate was decent. The days were cooler, and a few of the nights got uncomfortably cold/windy at points. Otherwise, another solid time to visit. Still wasn't as ideal as my late Sep/early Oct. trip. The stars were awesome, but only about half as visible, and trails were pretty crowded at points.
Sidenote: Ted, I'm in. I told you this! Haha. I don't care if I have to push the 80 or buy another one, I won't miss it for the world. My Graduation from CU is in May. I'm taking the 80 back to Colorado and spending a week or two wheeling/camping with the parents after. Then headed Toward Alaska and taking my sweet-ass time. Won't be back until I'm near flat-broke or tired of sleeping in my truck. (Month?). As much as I love the idea of hitting Moab on the way back from 12,000 + mile trip, I'll probably be low on funds, in no mood to sweat my balls off for two weeks and a little weary of my rigs condition. If the date DOES get moved to June/July, I will figure out a way to be there.
To conclude: September/October dates FTW. Great climate, not too crowded, STARS... seriously, and access to a garage? Ted, I remember someone briefly filled me in on Grandpas, but I can't remember. Also, I was going to extend an invitation to a few Colorado guys (Rising Sun), and I feel like they are going to be more inclined to come for a few days in Sep/Oct versus summer. (They wouldn't mind staying somewhere other than Grandpas if the head count has to stay low.