I haven't gone through and beaten all the expert ghosts yet, done about half so far, been spending more time trying to work on the 3* ranking (bout halfway there, Mirror is gonna kill me though) and getting my VR up (somewhere around 8300 now and climbing consistantly, just need more play time on it).. also, when I do the ghosts, I just keep reseting if I screw up more than I think I should, even if I'm ahead of the expert ghost.. I try to get the best time I can, not "just" beat the expert guy. Used Funky + Flame Runner for most of them, Funky + Spear for a few, Daisy + Mach Bike for a couple (more recently). Using a proper line with sharp turns and using shortcuts the best you can saves you the most time. Inside drifting bike is more or less a must, with a couple possible exceptions. I recommend watching the WR guys, and try to go from there.. copy them to the best of your ability

On Moo Moo Meadows make sure you keep turns to the inside as close as possible (really easy on this track), use the shortcut [edit: I mean mushrooming across the grass] on the last turn by the cows, don't use the ramp thats by itself right after that shortcut (still not sure about using the booster ramp, I think when I beat the expert ghost I used the ramp on one lap, because otherwise with my time I kept hitting the gopher guy on one of the laps, either second or third not sure).