As I play the flavors of Nestle's Toll House cookies through my mind, the main flavors are sugar, vanilla, dark chocolate and salt. The salt brings out the sweetness of the sugar and enhances the chocolate. The vanilla adds flavor depth. The flour acts as a vehicle to cary the other flavors, but has little flavor of its own. And of course the walnuts add there own distinctive flavor, which complements the vanilla.
That being said, you could substitute the shortening with unsalted butter to give the cookies a richer flavor. And as the baking soda realy doesn't cause these cookies to rise much, the fact that the butter melts faster shouldn't be a problem. Also, we double the amount of chocolate chips in when we make them in our home.
If you want gooey, as was stated above, undercook them by about a minute. Your nose will really tell you when they are done. When they smell like cookies, take them immediately out of the oven and place on paper towels to cool. If you cook them to the package directions, they will become crunchy, even though they seem soft when removed from the oven. They will also develop a "browned flour" flavor, which might be that nutty flavor you describe.
On the other side of the coin, if you substitute baking powder for the baking soda, the cookies will puff into a more cake-like texture. They will still be soft, but like a 'nilla wafer'.
I wouldn't play with the salt or sugar. Too much or to little salt creates a cullinary disaster. And the sugar adds body and flavor to the cookie. But I have made the more cake-like cookies using Splenda and they came out just fine.
For the gooey cookies, there is a very fine line between not well enough done, and just right. When done just right, they will still be shiny on top, but will have lost that liquid look. But remember, if they smell done, take 'em out.
Add an extra tsp. of vanilla if you have to, or more chocolate chips. And semi-sweet has more flavor than milk chocolate.
Hope this helps.
Seeeeeeya; Goodweed of the North