I don't have a dog anymore, but I found agility great training... for me! Roland, my dog at the time, I'm sure gained a lot from class too, but in our relationship I think I got more training out of it than he did. Additionally, classes of any sort, reinforce your procedure - maybe in your day to day life you don't need to use "Leave it" or my personal favorite "On by!" (keep moving, ignore xyz) - however in training (I went once a week for over a year) this is constantly done and reminds you not to get lazy and to THINK.

I like dogs, but I don't like being licked or jumped on or followed - and I'm very ... alpha-ish in dog language, which bothers some dogs - so I greatly appreciate your dog being on leash!