A few thoughts, consistent with what others have said:
If you want to go out and buy most of the "vintage equipment" that was used to record James Taylor's records in his heyday, you can do so. You'd better have tens of thousands of dollars to spend, though. Throw in the room as an item of "equipment," and make that hundreds of thousands. Just to elaborate further on a single detail: sure, James Taylor's records were recorded on a tape deck. To be more specific, they were probably recorded on Studer or Ampex machines running 2" or 1" tape at 30 ips, and the machines were carefully calibrated at regular intervals by qualified engineers. Whether recording to a 4-track cassette deck (or even a 1/2" 8-track) is "the same thing" is a question. They were also (I think) recorded with mics running through preamps and channel strips that, if anything, are more prized and more expensive now than they were then (and they certainly weren't inexpensive then).
On the "too clean and smooth" topic, there's a lot that could be said. The first thing I, anyway, would say is something like: "What? Vintage James Taylor doesn't sound clean and smooth to you?!" Maybe it's just me, but James Taylor records have never exactly sounded rough and edgy. There are any number of commercial releases today that sound rougher and dirtier than anything (at least anything non-live) released by James Taylor.
More on that: rough and dirty is actually kind of easy to get, no matter what recording technology you're using. Indeed, you're more likely to wind up with a recording that's rougher and dirtier than you want than the reverse (and, even if you don't, it's not that hard to dirty-up a recording on a computer).
There are various things you can do to make a recording more clean and smooth than it otherwise would be (and, indeed, more clean and smooth than what you'd hear if you were just sitting in the room listening to the musician play). Doing those things requires a variable combination of equipment, expertise and time/attention. In the '70s, the combinations that worked really well generally required one or all of equipment and expertise that only professional studios had, and a fair amount of work. Just a few examples: what are now "vintage" compressors, tape machines with the capability to do seamless punch-ins, the chamber reverb in the Capitol Records basement, the ability and time to edit single tracks on a tape with a razor blade, etc. Nowadays, tools with the approximate equivalent effect are availabe to pretty much anyone. The expertise is still an issue, but at least you can do edits without the possibility of requiring stitches.
The result, perhaps, is that - at least in some circles - people are going further toward "clean and smooth" than they used to. Like whoever makes Katy Perry's records, or whatever (I might be wrong there, as I'm less familiar with Katy Perry records than I perhaps should be). Too far? That's a matter of taste I suppose. In any event, there's an easy way to fix the problem: don't do so much.
A whole other topic, hearkening back to the first: James Taylor, to be technically correct though perhaps pedantic, doesn't play folk music. He plays folk-style music. The distinction might sound subtle, but it would make some people jump up and down about 40 years ago. Real "older folk music" sounds different (and was written and performed by "folk," not by guys with handsome recording contracts playing in arenas). More to the subject of the thread, there are recordings of real folk-folk-folk music in existence that sound quite different, from a technical standpoint, than your typical modern recording (and also quite different from any James Taylor record I've ever heard, so maybe I'm completely off topic here). If you want the sound of WPA recordings, you'll have to get a portable disk recorder. If you want to simulate that sound, there are ways to do it on a computer.
Anyway, my opinion on the "how do I make a '70s James Taylor record today" would be:
- Basic, everyday recording equipment will get you in the ballpark. In particular, you don't need a lot of channels, which is good.
- I'd put more attention and resources into the guitar than the recording equipment.
- I'd put even more attention and resources into singing and songwriting.
