I am so glad to see this question
I cut mine way back 2 years ago,( I saw that the local winery had done this) but the following year we didn't get any grapes to speak of. I left them alone and they are loaded again this year (Concord grapes.) My vines came from a start from some old vines my late mol had for many years.These are about 8 years old. There are always takers for these grapes if I have too many,
I don't mind sharing with the birds, for I still have a little jelly and juice from 2 years ago , when I kept my whole harvest and put up a lot.
PS. Your vines are a beautiful and a clever way to shade your AC.