I did not find the traders too much of a nuisance although they often left no room for musicians to play. However, you could always accidently kick their stall over while executing a perfect hook leg or galley ;-)
Call me an old cynic about EDDC consents but I suspect that they would take the money off those who would pay then conveniently not police the rest. More money for them and nothing would change on the seafront. They could police it under existing arrangements but they don't.
More of a nuisance were the street entertainers and musicians. The ever present pan pipers drowned out everything with their amplified music. The jugglers etc milked the crowds and were hard to dislodge for official festival displays (some of them got quite aggressive when asked to move on). Sadly, the general public saw them all as part of the festival when really they were just riding on the festival's back for financial reasons.