Since my gardens since moving to VA have always been made up of 100% compost, I couldn't agree with you more about that point. Well-made compost is loose & airy, yet holds moisture & is full of natural nutrients. What more could a plant ask for?
As far as Mel Bartholemew's "square gardening" system, I have to say that I still believe it's nothing more than an architectural/structural offshoot of the old "French Intensive" gardening system, which is what I use. And yes it's true that I think old Mel does sometimes take things to extremes without taking into consideration the habits of certain plants. But, what I can say - Mel's famous & I'm not - lol.
I am surprised about your Broccoli output, as I've always had excellent production with close-spaced Broccoli - even with lettuce interplanted between/underneath them. Nice big heads & lots of sideshoots afterwards. Same goes for Brussels Sprouts (except for the sideshoots, of course). Haven't been brave enough to try Cauliflower here in VA.
And I'm really surprised about your salad greens. I've been hard put to keep up with them, but then I don't go in big for the heading types - tend to keep to loose-leafs, mesclun mixes, & Asian greens that can also be used in stirfries.
But I definitely agree with you about the lack of weeds!! I'm willing to put up with any drawbacks of SQF or French Intensive gardening just for the delight of having to spend so little time weeding!!