Re: Why is Speed so unpopular?
I see pros and cons to speed.
The main con I see to speed is that big spreads can 1) be hard to manage, and 2) allows characters on the high end too much "face time." Its also a relatively expensive and limited way of modelling some "speedster" or "fast combatant" effects. There are other ways to model those things using powers, modifiers, etc. that don't automatically give the players of speedsters and their ilk more "face time" than other players.
On the plus side, I'm used to the speed chart and like the way it deals with recoveries. I also think its an excellent way of giving leading characters an modest edge and more face time - insofar is the spread remains reasonable.
My games - which are all heroic - tend to use set speeds based on drama ratings.
Extras, Bit Parts, and Mooks are Speed 2
Recurring Cast and Henchmen are Speed 3
Protagonists (PCs), the Big Bad, and his "Dragons" (e.g., Vader to Palpatine) are Speed 4
For supers I would expand the range to include Speed 5 for "fast guys," but would tell players to model "speedster" FX using other mechanics.