DIY Speaker Kits, a good idea?

"However, the typical audiophile mantra is to demo for yourself to find what subjectively “resonates” with you.  Can’t do this with a kit."

Not true in all cases.  The GR Research forum on audiocircle has a sticky up on top where people offer auditions of the speakers they've built. There's lots of people willing to help, if you're interested enough to pursue an audition.

I haven't chased it down, but I'd be surprised if CSS didn't offer some way of hearing their speakers before ordering.  

"Usually it's the box that is hard to make. A strong, non resonating speaker cabinet takes a lot of bracing and wood working skills."

..well, we definitely don't want to try anything outside our little bubbles.  CNC-cut flat packs are offered from the two kit vendors mentioned above. It only takes modest skills, and a minor amount of common tools, to assemble them.  People (that have never done it before) do it all time. You just have to want to do it.  There are a ton of build threads on the GR Research forum.  CSS builds are discussed on other forums(parts express, what's the best..). 

Resale..yep, there is a market(usually within audio forums as they are familiar with the models and vendor), but it'll be harder than selling a name-brand speaker.  But, say you buy a name-brand speaker for..$10K.  That speaker has..I don't know..$2500 worth of parts in it??  Then one day you need to move on from that $10K speaker and sell them for...$6K?  Well, that $4K hit you just took more than covers the cost of a very good kit.  So, the moral of the story is we all need to pay to play. You can buy a speaker kit for $2-$3K (that'll sound like a $7-$10K set of speakers) and sell it eventually, after enjoying them for years, for.. $1500? Seems like a similar story compared to the buying and selling of a name-brand speaker. 

Disclosure..I'm currently building an older model (offered & popular 12+ years ago) GR Research speaker (Super V) from scratch, no flat pack.  I'm a somewhat seasoned woodworker.  I've seen a number of sets of these built up Super V kits sell over the years for around $2K+.  The parts for this speaker kit didn't cost much more than that. 

All of the info I've offered here is on the web if you do some searching. 

The key to having some resale is to pick a very good model to build from a well known vendor. If you go with something too obscure then there's a limited number of people following the design or vendor and without a following..tougher resale. 

..yikes..lots of armchair, spit-balling going on here from folks that really haven't a clue, but are compelled to say..something, even if it's embarrassing.