Morrus said:"Super-hero" is tardemarked; "superhero" isn't. I've seen "superhero" used in lots of places quite freely, including supers games. It'll be fine. Although we may change the word "toolkit", purely for aesthetic reasons.
Yup, we could go for something like "The Slightly Below Average Suphero Toolkit", but I somehow don't think that would sell so well....
FWIW, I would definitely buy something called "The Ultimate Superhero Toolkit", because, that's what I'd most want from a D20 Supers product. I want something modular and plug-in-able and adjustable to handle everything from Daredevil to the Wesinger-era Superman. I want to be able to give a Mind Flayer 6 levels of the Brick class, or create a Wookie with fire powers.