"But consider that D&D evolved from tabletop wargaming, I always felt that the spell system was built on that concept and never evolved ..."
That is an interesting idea. Spells first appeared in the Fantasy Supplement to the original "Chainmail" tabletop wargame, which you can download from the internet archives. There were no spell slots at all, but there were five mage class levels which affected the potency and range of the spells as well as an ability to counter-spell. All the spells from Chainmail made it into D&D, and it's interesting to see where the basic D&D spells came from, and how little they have changed over the five editions. It might be cool to take that original Chainmail system and expand upon it, sort of like the warlock in NWN II but without all that evil stuff.
