Taste in sound is like taste in ice cream. I like vanilla, but you might like maple walnut, and I can't stand the stuff. That doesn't mean you are wrong, just that you have different tastes. I like "detailed" sound and gravitate towards detailed gear. Other people want "silky smooth". Until you get an idea of what you actually like, I wouldn't spend large sums of money.
The other thing to keep in mind is that some mics and preamps go together like peanut butter and jelly, and some don't. To me, it's the combo that makes the sound, not just the mic. Once you pick your mics, make sure you choose a pre that sounds good with those mics. AKG480's are good mics with some pres. An M248 pre is great with some mics, but I don't like AKG480's with an M248 as a combo.
Ref... buying used... I currently own, and have owned, lots of different mics. I've bought almost all of them from the Yard Sale, or from our "Team suppliers" like Church Audio, and I wouldn't do it any other way. Buying used off Ebay can be sketchy, but buying from the yard sale is a completely different story. If someone has a good history here and can supply samples "These exact mics made this recording on the archive", then it's pretty safe. If you can't get samples or the guy seems sketchy, then perhaps it's best to be cautious.
Personally, I don't think the upgrade bug is a bad thing, at least not for some people. I've been through a lot of different gear in the last few years, and that's how I've learned what works for my tastes. It can be an expensive game of trial and error, but it doesn't always have to be. You buy a set of C4's or Nak 300's for $200 and then want to upgrade... chances are you can sell those C4's for $200 (or maybe $175) a while later and you haven't taken a big loss. That's not always the case with all gear, but with some gear it is.