Oh I wouldn't want them for this, I'd want them for normal sessions. =P Adding a bunch of hit/glitch dice would be nice for Mini-Runs (Miniature-sessions).
Anyway, there's a limit to how much I can share without violating the NDA, but what I can (probably) tell is: In playtesting, yes sometimes we had too few dice, but that was before they tuned the game to wrap up faster (quicker Missions, just 4 Stages for a Final Mission*, less cards), and of course Veteran Dice helps (5+ dice become 2 less and a success). I'd consider it very rare now to get that high that you need to roll more than it gives you. So yeah, you don't need extra dice, but it's Shadowrun. It's not about needing. It's about wanting.
And yeah, there's only a few Face dice, but you only need that many, really. Faces are mostly just for giving benefits, not much significance in missions and very hard to come by compared to other dice. Their main benefit in Missions tends to be hoping to score a hit you can cancel an injury with.
* In the kickstarter, on the main page they show a 6-Stage Final Mission, while in the Rulebook you see a 4-Stage Final Mission. The 6-Stage is pre-nerf and the image will be updated in the future. You can imagine that 6 vs 4 Stages really makes a big difference.