Every tire has maximum PSI printed on the sidewall and I think it is rated as cold tire pressure, but still I would pump it bellow the number to allow for warmer temperatures and tire heating up while driving. As long as the pressure is bellow maximum, you should be fine, but it will make the ride stiffer and it could affect traction a little, especially in the rain, but otherwise you should be fine. The vibration was caused by tire not being balanced and that should not affect anything, especially that you didn't drive for too long with vibration being present. If you want to sacrifice a little comfort with better MPG, just increase tire pressure, it is probably one of the biggest and easiest ways to increase MPG in any car. Your tire guy is old school, where 28-32 PSI was the norm. Keep in mind, the famous Firestone tire blow ups in some SUV's few years ago were caused by low tire pressure, not high. FYI, the spare tire in your trunk is rated for 60 PSI, but it is designed as such.