Floorstanders - some design issues
You raise many interesting questions here, and I'll just touch on one or two answers for now.
The first one is - if I'm completely honest - that my entire experience is with "BBC thin-wall cabinets" which, by definition means "bookshelf" (= needing a stand or bracket, not actually being on a book shelf). I know a fair bit about how these cabinets resonate, how their resonances can be beneficially steered etc. etc.. For me, anything that strays too far from that well trodden path draws on a skill set that I just don't have.
Are there any really outstanding tower speakers? Does any professional sound engineer use a tower speaker at any stage of the recording/broadcast process? Do they have any technical or acoustic advantages over "bookshelf" speakers, other, perhaps, than stability on the floor as you mention?
As far as I can determine, if you put sound quality first and you have the budget to invest in an up-market "bookshelf" then you probably are not going to be seduced by tower speakers unless you buy with your eyes, as many do.
Alan A. Shaw
Harbeth Audio UK