What is cost-effective, what is a must have? What is just hype?
I really haven't run into much pure "hype" with this - except where folks will skew their marketing to confuse the issue between "sound treatment" and "sound proofing". I'm reading your post to be all about "sound proofing".
So staying focused on that - "What is cost-effective, what is a must have?" - without at all trying to sound flip, it all depends on what you are - specifically - trying to accomplish.
There is no getting around - compared to normal residential construction - increased sound-proofing is expensive... in materials, labor and space required.
And the lower pitched and louder the noise you are trying to contain is - the more expensive it gets. And if containing it somewhat costs "x", then containing a bit more can cost "x" times 2, and a bit more... "x" times 10.
Sad to say - it don't get much louder and lower than bass drums - so drums start from square one as being pretty demanding. With the big variable being, how much minimizing of sound do you desire? Need? And then of course, are willing to pay for.
I guess what I'm getting at is - try and answer that question first - even if it just in the realm of do I want a) someone in the adjacent to not even know I'm playing the drums, b) know I'm playing, but make it seem like a soft stereo being played in the next room, c) or seem like a loud stereo, d) a loud stereo at the other end of the house, e) a loud stereo being played next door from my neighbors point of views
Each of these a-e get easier and less expensive to accomplish - so knowing what you're shooting for will then set-up which questions about materials and techniques to get answers for.
From a new construction stand point, I would say your most pressing need if even considering going double-wall - would be obviously starting with a larger room than you want to end up with - and big time... a higher ceiling. (and there is no doubt that your best results can be achieved with double-wall construction.
But if you were to not opt for that, then a great compromise (and one that very much effects you initial construction) would be to build your walls with staggered studs on 2x6 top and sole plates. And big chunk of double walls capabilities - for a lot less labor, materials and space. You'll still want/need that higher ceiling either way.
Hope that helps,