Yeah, I had maybe a 2-second delay, and I didn't like how it sounded with feedback close to 100%. I thought it was too dense, without enough space. But if I made it longer, there would be more room for silence or some sort of negative space.
Also your comment gave me another idea: I think I'll use the delay to build up a looping backdrop and then stop feeding sound into it so I can solo over the background, or put other instruments over it in kind of a Terry Riley fashion. Also I could make several loops for different chords and switch between them. And then if I want to play another sound over it, I can switch~ off the waveguide-feedback subpatcher and just leave the delay or looping table running.