Yeah, they're not as great for the normal waves anymore sadly. There was a build where their spawns was more random, and using the cart to clear the screen felt like it could be more worth it.
On the other hand, if you noticed with the boss. It actually starts with a BossWaffle counter! So the faster you kill it, the more waffles you get from it. And especially with the rapidshots it delivers, you can easily mow through it with the cart.
But you're certainly right, it could've used a few more incentives on that. Thanks for the tip ♥