I went through a stage a few years back, while searching for "a better sound", where I was buying up every "new to the market" microphone that came out, it seemed...but my recordings never seemed to improve that much... Basically what I ended up with just "more of what didn't sound good" on my recordings...
My story is similar, only things did improve quite a bit with many of the mics. It helps to start with mics that suck badly enough so there's room to upgrade.
Okay, and my room isn't too bad, either.
I find that some sources are more sensitive to mic changes than others:
- Drum overheads are exceptionally sensitive to bad mics because they have to produce a stereo image... and because cymbals are very bright, so hyped mics make you want to rip your ears off.
- Vocal mics for the lead vocalist are really critical because it has to sit out in front of the mix and sound good.
- If you are doing a relatively thin mix, everything matters, and acoustic guitar is about the most sensitive in that case. If it is buried as a rhythm guitar track in a thick rock mix, though, not so much.
Everything else... basically is background noise, and you could mic it using a cheap pair of Wal-Mart headphones as a mic through 1970s TEAC cassette recorder pres and it will still sound good.
I don't think it is so much that there's a point of diminishing returns with mics so much as that there is a point at which something else becomes the biggest problem.
It's like fixing up a house. You conclude that the bathroom needs work, so you spend $10,000 to upgrade the bathroom. Nobody buys the house, however, because the front porch is falling down. It is not sufficient to have one incredible part of the signal path if the other parts are bad. Great microphones still require at least passable pres, passable converters, and a passable room (and a passable engineer, of course) in order to reach their full potential.
In other words, the money you spent on mics isn't wasted. It's just that you could not recognize the differences in those mics because they were so thoroughly masked by other problems, much as the potential home buyers could not recognize how much the bathroom was improved because it was so thoroughly masked by the fear of falling to their deaths through the rotting porch boards.
