When deciding on purchasing a vintage Omega, one of the decisions I have to make, is whether I want consider the whole series or stick with the 24 jewel versions. I tend to lean toward the higher jewel versions. I'm looking to get the watch I should have purchased shortly after I joined the Army in 1973. At that time there were still a lot of 550s available at good prices. If I'm brutally honest, a 550 ref 165.0023, is probably what I would have purchased. Would I really gain much holding out for a 552, I starting to think I should grab the first one I find in acceptable shape that I find that appeals to me.
Desmond wrote a very detailed piece on the mid-500 calibres that is well worth a read if you haven't already: http://users.tpg.com.au/mondodec/movement3.pdf Have to say I love the 552 in my SM300, I never wind it, and don't wear it very continuously but somehow the winding efficiency of the thing just keeps it running.
I think most of the extra jewels are in the automatic winding system, making it more efficient and durable because of less friction. I wouldn't call it settling for a 550 over a 552 since the extra jewels shouldn't be a deal breaker. The single most important part of a vintage Omega is the dial - original and as close to mint as possible is what you should look for. That can be 30% to 40% of the value of the brand's more sought after watches.