I realize "worth it" is subjective... so what are the differences on the engine side? Many TMCC have speed control, have more than 32 speed steps if using ERR, TAS etc... I read that the Cab-2 much improves even the TMCC engine control. I have not found a breakdown of the Legacy only features here or on other forums (if there is one, I vote for Sticky!) An extra $100+ for a quilling whistle doesn't seem worth it to me.
I am just getting into command control and have a Legacy 990 on order. I realize the advantages of Legacy there. Now on to deciding what engines to acquire...