Would the large vehicle calibration be any less accurate compared to normal compass calibration, which you do by rotating the vehicle? And how important would a motor magcal be in general?
Sorry I am not too familiar with how these 2 are executed. Would really appreciate any insights here. Thanks!
Yes, it is less detailed and less accurate.
Depends on the level of magnetic correlation/coupling between your electrical current and your compass.
That is dependent on your vehicle. There is no single general answer for all vehicles.
The real question is how valuable is your drone? Is it valuable enough for you to care and do the calibration, or not?
IMHO Cutting corners is the safest path into undesired surprises. 
Fair enough, I guess I will be sticking to the spinny method (RIP my arms). Thank you!
I would do magfit from flight log if You have GPS, or in case of large vehicle dual antenna GPS for heading might be best option.