With the money we are saving staying in a Disney Springs hotel, which is almost half of what we would have paid at a moderate, we figure using Uber/Lyft will be very affordable. We will try the buses, too, so it will be a combination of both.
With 5 people, I'd look into an Uber XL (not sure Lyft - I've only used it a handful of times). That way you'd get a vehicle that's large enough.
I totally agree with your thinking. If I were at a Disney Springs hotel, I'd Uber/Lyft rather than use the bus they provide. Note: for MK, get dropped off at the Contemporary rather than TTC.
What about uber/lyft to the parks (MK go to CR) and take the Disney Springs bus back to the Disney Springs hotel ?
Might be the best least expensive way
Why rush back to a Disney Springs hotel ?
Even if you have to wait 20 minutes for the bus ride back, you can enjoy the great times you had in the WDW park and the snack you just bought to much on the way back to the Disney Springs resort