This isn't much help for the bedroom producer, but the unfortunate answer is: really good microphones in some of the world's best rooms.
The challenge of recording acoustic guitars is that they're, well, acoustic. As with violins and celli and hammered dulcimers,
the room is half the equation. You need the difficult-to-achieve combination of a reverberant space that lacks discernable resonances. You can't get that in a small or square room, and you can't get it in a room with lots of acoustical absorption. IOW, the typical home studio.
What you can do is start with a microphone that does well at high frequencies. An SM-58 won't cut it. Ideally it'd be a small-diaphragm condenser, but any high-quality condenser microphone will work, preferably a multi-pattern model that will let you set it to omnidirectional mode. That eliminates the proximity effect while allowing more of the room reflections in.
Avoid some of the guitar's own uneven resonances by avoiding the "sound hole". The desirable sound of an acoustic guitar emanates from its top plate, not the hole. That's why most miking techniques have you pointing the mic somewhere between the neck and the hole. Experiment with how far away you can get the microphone before it starts sounding thin and nasty. The better the room, the farther you'll be able to place it.
Because your room probably doesn't sound like EMI studios (and whose does?), use acoustical absorption to dampen reflections and make your room sound more neutral. It's a meat-axe solution, but the only option available for most of us. You'll just have to make up the lack of ambiance with artificial reverb.
Oh, and one more thought...fresh strings make a huge difference on steel-string guitars. Yeh, you'll have to constantly re-tune it but they'll be much brighter.