just to add even more questions, are the songs just acoustic guitars and/or vocals or are they going into a full band mix? what style of music is it (i.e is it big open chords, altered tunings, hard strum stuff, or is it power chords and chugging rock acoustic stuff?)
alot of my acoustic playing is pretty hard hitting/aggressive and i've found a couple of ways of improving my recordings;
Firstly, and especially with acoustic guitars, if it sounds good in the room it should sound good recorded.
Secondly, and hopefully an obvious point, new guitar strings. old strings sound flat and empty.
Thirdly, i've found using a thicker plectrum gives a much attack and really helps gives an "aggressive edge". i recorded a guy at the end of last year who had very dynamic songs but found that when the acoustic guitar shifted from the quiet parts to the louder parts it just sounded flat and weak. the answer; rather than using his 0.6mm plectrum we swapped it for a 1.0mm pick and suddenly the loud parts has a real impact
in terms of mic's and mic placement; the 12 @ 12 is always my starting point. because i have a smaller bodied acoustic (Taylor Big Baby) i normally find that works fine, although sometimes i move it more towards the neck joint. however, on full sized guitars with hard hitters i normally pull it back a bit.
I'm a big fan of LDC's on acoustic guitars most of the time, but opt for an SDC if the guitar is going into a very busy mix to let the highs come through a bit more. again, in terms of polar patterns, if the room sounds good i really like an omni mic, but with my style of harder playing i normally stick with a cardioid mic to get a more solid sound.
if the 12 @ 12 sounds too thin/weak (even after experimenting) i sometimes add another mic pointed just about 3 - 4 inches below the bridge to thicken up the sound. however, if you do go down the two mic route you do need to be very careful with phase issue. realistically you should be able to get a really solid sound from just one mic.