I was really dissappointed in the first of the "Second Foundation Trilogy". The other two books were better (and I noticed that passage you quoted there), but I feel like "Foundation and Chaos" and "Foundation's Triumph" had to spend a lot of time to try to fix the problems from the first book (wormholes, really???).
Still want to see a book that takes place after "Foundation and Earth", though. I would recommend an eventual merging of the first and second foundation.
You're looking for Psychohistorical Crisis by Donald Kingsbury.
It takes place after the second galactic empire came into being, dealing with a crisis that is both a logical consequence of psychohistory and its achilles' heel, and you won't find any wormholes (or robots) in the book.
PS - I see the recommendation has already been made. Twice!
Well, now it's 3 times.