Re: mystery SELMER Alto #534xx marked "NEW YORK"
This is a nice, New Wonder model horn(Ihaven't seen your horn, but it is more than likely a Series I model). It is perhaps more desirable to Selmer (and Conn for that matter) collectors to fill in a collection's history line of horns, than to the contemporary player, except for those looking for a superior example of the "New Wonder" type horn to play(And there are some of us out here!).
With BA, SBA, and MkVI models as the most desirable by the majority, with maybe the Jimmy Dorsey model as a distant second; models like the New York, Manhattan, 22, reg "Cigar Cutter" models etc. don't seem to command as high a price, with rare exceptions.
Although I have a number of Selmers in my collection, I am not an authority on them, and feel a number of other posters on this thread might be of better service in evaluating your horn's worth.
I will say that most "Experts" who might be in a position to purchase your horn (i.e. Vendors) also tend to charge a fee to appraise a horn, so hopefully someone will step up and help you out on this forum. Cheers and best of luck. Mike.