How will my document get from my device to my printer's e-mail port? Will it simply move directly from my device through my home router to my printer? Or will it wander off to the "cloud" someplace before making its way back to my printer?

I don't see an issue with Spam. A couple simple mail rules will make this an easy product to utilize.
Use mail forwarding if you don't have controll over a mail server to set your rules. Use rules by: Sender, and subject (use subject as a password). You will likely never see a spam print.
As for the particality of the product, I guess there is a market for anything.

How exactly will one set the print settings? Ever try printing an oversized Excel spreadsheet or a Visio diagram and have it fit into a page without tinkering with print preview for an hour?

P.S. Looking forward to having "GET A BIGGER PEN15!!" printouts come out from my printer.

"Will you're HP Photosmart receive spam from the Nigerian consulate for an interesting business proposition?"

I am not a printer.

that we'd all still be riding horses.

But there has to be a limit put on needless "technological" silliness somewhere, and I propose that *this* be it.