Hi all, I'm a '74 Classic operator, and yes, I still think they are the best, anyway -
the initial spool-up is for mainly the assurance that when the time comes to set take-off power, especially when the bird is light, all the engines have actually spooled up, and the aircraft keeps heading in the right direction!
Also, we have actual real eyes watching all the engine instrumentation, in addition to comparing both sides flight instruments, good eh!!