We go every August and have been for the past 11 years now and I think it is the perfect time of year but unfortunately everyone else is figuring that out as well. When we started going to Ouray in 2007 the campground that we stay at was only about half full and we would see a few Jeeps and a few ATV's on the trails here and there but the weather was fantastic and usually the snow was just melting on an above average snowfall year. Most years there are a few traces of snow here and there but nothing is impassable.
In August 2017 this was a common site on several of the trails.
This past August (2018) was the warmest of the years that we have been going because we had to run our rooftop A/C's in our coach for the first time in all of those years as it was in the mid-90's, unseasonably warm for the area. The rivers and waterfalls were also at their lowest so the scenery was not as breathtaking as usual.
As the years have gone by we have seen an increase in campgrounds being full and last year when my wife and I hosted our annual rally there the campground had a waiting list for several months prior and most others in the area were full as well. Also last year was the first time that we had a 2 hour wait lines up above the waterfall on Black Bear Pass with about 25 vehicles ahead of us and many a bit nervous of the switchbacks which just prolonged the wait. Heading back over Imogene Pass the two way traffic seemed to occur at the narrowest and most inconvenient times which made the wife a bit nervous as it seemed to keep putting her side on the downhill side. Even on Poughkeepsie it was a heavy traffic day and by the time we arrived at the "wall" there were a good 20 Jeeps ahead of our group of 12 so a long wait at the end of that trail as well.
All in all it is still fun and great time of year to go but the traffic from the Jeeps has increased and the amount of side by sides on the trails now is almost enough to make a person pause and rethink the August timeframe. We have some friends that have gone back in September a few times and think it is less crowed but the weather is a bit more unpredictable that late in the year.
Mike