Those Fan Surveys that are taken every day after a game determine ticket and merchandise sales. Having a better PR guy will give you better results for those so I'd say it's most essential to have a good PR guy when you're struggling to fill seats or if you expect to struggle in the near future.
Also, the National Appeal/Crowd Involvement specialties can directly improve your team's play regardless of the PR guy's level, so if you dont need lots of PR it still might not be a bad idea to pick up a cheap level 2 PR guy with one of those specialties.
(National Appeal = Road game improvement, Crowd Involvement = Home game improvement)