As for gameplay expansion - I do not think C&C could use it, I think it desperately needs it because of how basic the gameplay for a casual person (like it or not - majority of potential customers) is.
For the "fast gameplay" thing:
Is C&C really that fast?
Sure, EALA told us CnC is "fast, fluid n' fun", but that was just e-sport wannabie PR for TW. Were the C&C games that fast?
TD & RA - Slow, slower than Warcraft and Starcraft
TS - One of the slowest RTS games I played, even when on max speed.
RA 2 - Finally something faster and more "arcade".
Generals - Game of rather medium speed, it could get very slow, positional and tactical when played well in such fashion.
In my opinion, Tiberium Wars was the "first" really fast C&C game. It was never a major part of the series' gameplay.