I've unlocked Eggman, joyous day!
It was beating all the cups by the way in case anyone was wondering.
I'm still thinking that the Nights track is a pile of poop, I was using Aiai and it felt damn near impossible to catch up because of the racers with a higher top speed, I was hitting every ring but barely closing the gap, the brief water section was the only point when I could make some progress and the warp point and plane transformation areas occasionally seemed to fling me into the wall like i'd lost control.
I'd say the third cup is the weakest on the whole, the last two tracks are good fun but even then Sky Sanctuary I feel is far more enjoyable on the second lap when the plane buggers off for a bit.
Unlocking the expert difficulty applies to the world tour as well it would seem so now there's even harder challenges and even more stars, don't think i'm aiming for that 100%
On that point i'm loving the stickers/small scale trophies, there the sort of thing you just end up doing in a race and feeling pretty chuffed about.