As a working professional (straight-ahead jazz and teaching) who has a YAS 23 and a YAS 52 (the American model for the 32 I believe) as my only two horns, I can tell you they are slightly different. I personally prefer the 23. It is a lightweight, responsive horn with comfortable ergonomics and excellent tuning. It's also easy to keep in good regulation. It leans towards a clear "West Coast" kind of lightweight tone that is good for bebop, swing, and classical, but doesn't lend itself to the kind of depth and "guts" most blues and rock players want; it gets a little bit shrill and piercing if you really push it. Of course this kind of thing is most impacted by technique and mouthpiece, but compared to other saxes that's how I'd describe the 23.
The 52 is pretty much the same with slightly more weight and a feeling of solidity both under the fingers and in how it blows. It is also slightly brighter, slightly more focused, and slightly more resistant, and holds together a little better at maximum volume. The ergonomics are awesome - for me the LH pinky keys are the simplest most elegant and comfortable design of any horn I've ever played. The high F# is not important to me at all but it is to some people.
For me the best investment in equipment is the mouthpiece/reed combo, followed by keeping the horn well regulated; an airtight 23 is better than a leaky Mark VI 100% of the time. So spending 500-700 Euros to have it totally overhauled would likely give you a better playing horn than buying a "superior" model that is not in totally ideal condition. You can also "upgrade" the neck to any of the Yamaha necks (and most Selmer/Yanagisawa/Eastern Music or whatever necks will work too) which is relatively inexpensive and does have a noticeable impact on tone and response.
Having said that, if you do want to look at an upgrade to a YAS 52, 32, 475, 480, or whatever, the biggest piece of advice I can give you is to make sure it's made in Japan. The newer horns made in Indonesia or wherever are pretty good but don't garner the same consistency of praise and probably have a lower resale value.