Ok - I'll spill my secrets (why people buy vintage Paiste). Disclosure - going to limit to what I have owned/flipped at one time or another.
My first exposure to Paistes were a set of 400s in the high school jazz band. Upon research last year, I discovered that they were a brand new line at the time we bought them. I thought they were decent, but was aware that they were not the best Paistes out there. I wish they would have bought 505s at the time - which are a bit better.
Now, some may say I am crazy, saying that 505s are only a 'bit' better - but the fact is.....of the 400s....they are made of the same alloy - but, in Paiste fashion (which makes them so good at making cymbals) is that the lathing is different. There are many Paiste lines with the same 2002 alloy - but what makes the difference is the lathing. I actually like 400s and think they are actually very good cymbals - but beware - that they simply sound different. I don't think they mix all that well with 505s (for example) as there is that distinct sound difference - but I must qualify - that I believe they are better described as different when comparing to other lines (as opposed to better or worse).
Now, 404s - these are sleepers, but you must know the difference between them and 505s or other better quality cymbals. Fact is, the 404s were the bottom of the barrel at the time - but the reason why you still see them going for some good dough now and see pros using them (many jazz cats) is that they are thinner and therefore darker - but don't think they are dull sounding at all. I have some 404 crashes and they are bright as ever and very cutting - as that's just it - they cut like crazy - best way to describe them is that they are very focused with a more narrow frequency range and therefore less complex as the 505s. Don't be fool to think that 404 crashes are not as good as the 505s, but know that they are less complex and much more focused. The 404 ride is a particularly good cymbal, though I do not have one. Value per dollar - way up there.
Sound Creation and Dimensions are awesome, though I can not describe them like I have the 404s - but their great quality is reflected in their price.
505s are simply great......not too different from the 2002 (and in fact some prefer them to the 2002s) - but this secret is OUT and they are priced as if they are gold plated 2002s. Only buy if the seller has no clue or could care less how much they get out of it. Of course, you may get lucky and discover them in a flip deal (or any kit for that matter) you are buying - as that is how I discovered the 505s in the first place - and now my 505 is my main ride, replacing a 70s Zilly A.
Don't waste your time with 200s - all brass I believe. 302 HHs are surprisingly good, as long as they are the later generation (change year 1998 - with the scribbled font that sometimes people misread and try to sell POZs or SOZs (you get the idea - quite humorous actually!)
1000s, 2000s, 3000s - all great, but they have their own characteristics (read up on them at Wiki-Paiste- 3000s were heavier I believe.
Lastly - the easiest way to learn about Paistes without finding some huge collection of them to check out in person - is to view videos on Youtube by Terry Keating. His username there is bonzoleum and in my opinion is that he should be employed by Paiste - he is that knowledgeable.
John