I believe that there will be more than one Smash Ball per match. And if you put them on very high, they can still be rare. Remeber the Hammer in Melee? If you put only Hammers on very high, it still takes longer to appear than most items.
Anyways, I think that Zero Suit Samus might have a final smash in the form of the Crystal Flash from Super Metroid. Check it out:
http://www.youtube.com/watch?v=alepBscgUX0
Sakurai researches far back for character moves and history (see Volt Tackle), so I wouldnt doubt it. As you can see, Samus envelops herself in an orb of energy that replenishes her suit. Now for Brawl, it can be translated as Zero Suit Samus enveloping herself in a huge orb of energy that damages nearby foes for a while and when it is done, Samus has her suit back on (reconstructed by Crystal Flash).
I think this would be perfect for Zero Suit Samus' potential final smash, and aesthetically would look great too. Notice that you can see Samus within the suit, in that video?