Concentration is quite important, since it increases the opportunity cost of costing a particular spell (you can only concentrate on one spell at a time). Had a little shock when I saw you mention Grease + Concentration as I was using it a lot, and thought I missed something ^^

Grease does not require concentration (at least in my PHB it doesn't)

Background information doesn't necessarily have to be confined to 4th edition, as long as you explicitly mention from which edition it is, I'm fine with it.