I went last year and it was a great atmosphere. 26 of us cycled from Cherbourg over 3 days, we stayed in a novotel/etap at versailles which is far enough out to not be full but an easy trip in on the metro.
Don’t bother getting there early to get near the front, as you will get pushed back by French kids anyway. Definitely do find a stool or steps and stand at the back as you will get a much better view. It was about 7 people deep all up and down the Champs Elysees. Also you can turn up last minute after enjoying a relaxing morning in the bar, look at LA’s bike in the Nike store and get fleeced for a load of TdF tat. They don’t give out freebies on the circuit so you won’t miss anything there.
Definitely worth going if you are any sort of TdF fan though, and better than out on the stages as they come past 7 times.