That exception aside, we generally want our mic pres to be as clear and as clean as possible. So, you go out and get your entry level preamps when you're just starting out, and say to yourself, "Gee, they sound fine to me. I don't hear any noise. It sounds pretty clean. Why would I pay five times the price?" And then you splash out and spend five times the price and you hear it, and you think to yourself, "Gee, I guess it sounds better. But at five times the price, the difference is barely perceptible."
I mean, really... listen to the Behringer preamps and they do sound pretty darn good. A/B them against even a fairly semi-pro unit like my Steinberg MR816 ($1000 for 8 preamps - not exactly in the $1000 per channel just yet...), and you'll hear that "not as different as I might have thought" that I'm talking about.
What is important to understand is that the difference is cumulative. Record 16 channels with entry-level pres and you'll fight like heck with it to get it to where you want it to be - if you ever actually get it there. Record 16 channels with much better preamps, and the project will almost seem to mix itself.
Here's why. (click on the image to make it larger.)
THAT is the difference between entry level preamps and something you'll pay more for.