Is sneaking this stuff into foods making any consequential difference? It's probably more effective to go the opposite direction to make something less appealing become more so - e.g. adding cheese to some veggies, maybe oven roasting green beans, asparagus, etc.

Yup. It does change the taste. However, if you make sauces a certain way, your DC will be used to how it tastes. I also think roasted veggies have a deeper flavor. Maybe try roasting them first.

Also, I do a thin veneer of pureed squash in my cheese quesadillas. Too much and it does taste off.

Am starting to experiment with doing this and have noticed that it takes only a very little bit of the veggies before the food starts tasting very obviously like the veggie. For example, if I put squash or broccoli into marinara sauce, I'm surprised by how little squash I add before the taste of squash becomes (at least to me) very obvious. Has anyone else found this or am I doing something wrong?