Haven't heard the 30.7 yet, but I love the 3.7 and 20.7. It is true that all 3 of those models require a good-sized room. The beauty of Maggies is that if you have a smaller room... there are smaller Maggies which will integrate better... and sound better than a large model 'stuffed' into a tight space.
The one caveat with Maggies (which partially offsets their low prices) is that you need powerful amps to drive them properly. I'd recommend at least 200W/ch for the 3.7, and maybe more for the bigger ones.