What you're seeing sounds like very typical 7 year old behavior to me (at least it sounds a lot like my own children at 7 and most of the other 7 year olds I've known). I wouldn't worry about whether or not he sees the value in practicing new concepts at this age - that's something that will come with time, and also perhaps when it's *needed*. Does he have a math tutor because he's begging for more math? If he loves math, I'd let him go with it for now. He might have to come back for more reinforcement later on, but he's got time for that down the road. For now, let him enjoy learning the things he is interested in learning, even if it seems like that changes direction every few days.
Best wishes,
polarbear
ps - another thought that crossed my mind - you mentioned that he was really interested in quadratic equations and then that interest lapsed after 1-2 weeks... I'm not sure that any of the topics my kids cover in math in school really last longer than 1-2 weeks in duration - even quadratic equations. Everything builds on previous topics, but something new is also always being introduced. Even in Algebra and beyond. The thing I remember being repeated over and over again until my kids wanted to bang their collective heads against the wall was math facts
