You're going to get a lot of different opinions on the subject, which will likely vary a great deal. And they should, because it's a grey area. So much of it depends on how serious you are about your recording; what are your goals for it, and how strong is the rest of your signal chain? And what level are you at as an engineer? In other words, if you're just a semi-serious novice engineer, then what in the holy hell do you need a professional-level tool for? (Do you even have the necessary skills to put it to good use and derive benefit from it?)
What it all comes down to is individual need. So use whatever gets you the sound you want/need. If you don't know what that is, then see if you can rent a higher-end mic pre for a weekend. If you're too lazy to go that route, then 3D-audio has an entire CD that does nothing but compare different mic pres. The Listening Sessions is another good example (
www.thelisteningsessions.com). Do some comparisons between the nice ones and some other budget pres, and evaluate the finished products carefuly and decide from there if the added price is justified . . . or if it's an area you feel you can skimp on.
That said,
here's my opinion: I don't think the mic pre is where a home recordist should first start looking when it comes to upgrading your gear list. If you're getting paid for your work or striving to do this professionally, then I think you might start to see a payoff . . . but even then, I'd still advise upgrading/investing in the weakest and most important parts of your signal chain first. Having a really nice tube guitar amp on hand that records well . . . or having a nice Fender Jazz (American-made), precision, Musicman, etc. . . . or being able to hire a drum tech for the day . . . not to mention having a nice selection of mics and a killer monitoring system to listen and make decisions with . . .
these are all going to make a serious difference in your recordings.
Having nice mic pres to plug all this stuff in to is just extra icing on your cake.