Hmmmmmmmm . . . . . . some good ideas here. I love Velveeta mac & cheese, and if you like it, that's be the place to start. I'm on board with cooking onions and garlic when you brown the ground beef. Maybe some salt & pepper too, and other seasonings to taste. The pasta, beef, onion, and garlic all mixed together with the Velveeta ought to work just fine, bake or no bake.
I'd play with some other seasonings as well. I'm a big fan of Emeril's Southwestern Essence, which added to this would make Southwestern Cheeseburger Macaroni. I knew a guy that was a big fan of red pepper and cayenne, and put crushed red pepper and cayenne in just about everything.
Emeril's Essence (all varieties) is available at grocers, or the recipe(s) are available via Food Network.com or Emeril's website.
This is not inteded as a promo for Emeril. It's just a multi purpose seasoning I prefer.