This thread could probably be boiled down to a few main points.
- The ME driver who provides an extra service should absolutely be tipped. They handle your bags or provide some value added service that stands out - Tip! (Tip per bag for baggage handling or a flat rate for value added service.)
I have never seen anything that says you should tip your bus driver between the parks and the resorts. We don't. We also don't tip if the ME driver doesn't handle our bags or provide extra service beyond just driving us to the to the resort. Again if the ME driver does handle your bags or provide extra service ... it's a whole different thing.
- Servers -- If the server provides good/great service then US custom says tip... somewhere between 15 -25% based on the service (or more if the situation warrants it.) For some servers this means a great bonus for others it means a living wage (based on reduced minimum wage for servers and share-outs to other staff.) Most servers do their absolute best and I understand that sometimes that translates differently to the perception of the diner --- when kitchen issues arise, when staffing issues arise, etc.. Remember your server is an actual human being, working as hard as they possibly can to make sure you enjoy your meal/service.
- There are some positions which cannot accept tips at all -- this is a WDW thing --- not a should I or shouldn't I tip --- if this is the case ---- send an email or stop at guest services to let them know that a cast member went above and beyond (makes it safe for them --- since they can't take tips --- and lets the employer know that the CM provided great service that meant something to you.)
- Housekeepers --- they have one of the ickiest jobs... some people are clean and considerate others aren't. For me I tip every day --- $5 per day when I'm solo or $10 per day when we travel as a family (DH and DS). We never leave our room a mess. For all of us when we arrive at the resort the first day and want to get to our room early --- it's possible because Housekeeping has cleared those rooms so they are available.
There are others we tip as well --- bartenders, bell services, room services, hair stylists, taxi drivers, etc... but these tend to be situational... Had a taxi driver who literally drove on the sidewalk when pedestrians were there --- yeah, he thought he'd get a tip for getting us there sooner but didn't --- the whole endangering life and limb of the pedestrians was really a thing for us.
I think this boils down to this --- tipping is a US custom (it's also a custom in Canada where I'm from, although I think the minimum wage is slightly higher here --- but we still tip similarly anyway.) If you're a tourist in the US follow the customs and standards of where you visit -- tipping included.