Larry, You are posing some most interesting questions and I suspect you'll get several replies: all different. In order to go further you'd have to explain: why am I building this piece? Do I want to build a "replica" as nearly as is humanely possible, of an original period piece? Or do I want to make a nice piece "in the style of" or "close to" an original piece. Or do I want to build a piece using features of 18th century pieces but not necessarily following any individual piece. Or do I just want to build a table for my wife's porcelain collection, not being too concerned with what it looks like?
For the most part I want to be "close to" an original, or to look like a piece in a picture. In this case "scaled drawings" are a delightful luxury, but not a necessity. (Actually, scaled drawings are not necessarily perfectly scaled and even if so, scaled to what?) Scaling from a photograph is plenty sufficient though you will not be precisely accurate and you can easily add a half inch here, or cut a half inch there and keep pretty close to the "perfect proportions" that the Townsends and Goddards and others achieved. And you're right the phase of the moon might affect your efforts!
The basis for the question was what a magazine editor told me that his readers wanted measured drawings. To me that was odd. Since I am self taught and somewhat unskilled in that I make the first cut as close as I can. The rest I just sneak up on. There is no way that a cutting list would be of any use to me. In other words, the last cut would fit. But it would probably have little resemblance to the last cut on the drawing.
The thing about scaling from a photo is the wide variation that can result from a slight variation in one or more of the parts. What I strive for is something I learned in HS geometry. Proportion not finite measurement. But I could have dozed off that day.
I like to make reproductions, mostly because I don't have the skill to design my own piece, and I feel why bother, there are so many pieces I love why would I risk designing a bad piece when I can reproduce one I already know I like. I also plan on combining parts from different pieces. Such as putting chair A's legs on a chair with B's backsplat.
I see no problem with people designing things in the style of, since really that's all the builders were doing when they made original pieces.
Having said that I would like to have full scale drawings just because it would make reproducing easier. If possible I will increase a picture to full scale, print it out, and there I have my templates. But I agree cutting lists aren't that useful for anything other than to calculate how much wood you'll need. I usually plane a board until it's an even thickness, I don't care if it's 3/4 or 7/8 I just cut the corresponding piece to fit. Being an engineer it took me awhile to depart from exact measurements.
Everything, at least most things, are learned behavior. "Why bother" from someone that "learned" to be an engineer? Its true most of us don't have the ability, natural or learned, to be truly creative. But like you suggested it is fun at whatever level. My very first woodworking project was to cut our queen size bed in half to convert it to a king size. Even my wife said it turned out OK. Although for a while I thought it was going to be my bed.
If you look at the furniture books no two pieces of furniture are exactly the same even if they are made by the same cabinetmaker.
If you were an apprentice in the Townsend cabinet shop you would have been told to construct a block & shell bureau by the methods used by your master. After you finished your apprecticeship you could leave and start your own shop. If a customer order a b&s bureau wouldn't you want to make it in your own style and dim's? I would. Now you are independent and can make what ever you want.
My point is to use scaled drawings only as a guide. Change the dim's and style to suit your needs. If the original was 18" wide and your board is 17" wide then so be it.
When I was an apprentice (as a wood patternmaker) I told one journeymen that I want to be just like him when I finished by apprenticeship. He said NO! You want to be like me and Jack and John and Steve, etc. and develope your own style. A lesson for all of us.