Smarts is necessary at every point in both games. The smarter person (who understands the physics of the game, has knowledge of moves and their hitboxes, basic tech skill, etc) will probably win at any level of play in both games.
Knowing how the game works isn't part of the 'smarts' category. That's part of the technical category. Anything that relates to the game in a sense is technical. Smarts, is being able to outsmart your opponent via mind, not via game.
For example, L Cancelling. If one person knows how to L Cancel and the other doesn't. While the player who doesn't know how to L cancel might be smarter, the person who knows how to l cancel get get away with more pressure, because the lag on his moves are decreased dramatically, while the opponent doesn't have that advantage
Also, you said here.
I was going to post about how having smarts is much more important than tech skill in melee.
You're implying, that knowing what your opponent is going to do, is much more important than tech skill. So, in the situation (jiggs vs fox) you're smarter than your opponent and you know that your opponent will jump in and n-air, so you'll shield it and grab him for a u-throw rest (in brawl, this would be perfectly logical, considering you can powershield and all moves have lag to an extent)? Well, the fox l-cancel and shines on your shield, you just took damage thinking you would get the grab off. There are things that you technically speaking don't understand at certain points, therefore in the beginning of play, being technical is more important than being smart, then when things get even, being smart becomes more important.