We have been to YNP several times, so we would definitely stop again if we were in the area. The reasons to visit will still be there. Pay particular attention to the weather, it can snow in YNP any month, and I believe it snowed there this July at elevations above 10,000 feet. We were snowed in for a day one year in June, Park Rangers would not allow travel until the roads cleared.
As noted by others, things will be closing up by around mid-October, in and around the park. Make sure you are well stocked-up with food and water, and make sure there is ample cold weather gear on board.
Wish I was going with you. Have a great trip!
