A bit late, but the PSR550 had amazing speakers. It would be fun to collect just for the sake of it; but it's so old it used floppy disks, so don't expect to do much with it other than play it out of the box. (I assume you mean the 2001 PSR550, not the 2008 PSRs550; the latter's speakers were underwhelming, but at least it had a USB A port.
Plus the PSR550 used the older (lower rez but punchier) drums, so a lot of the beats actually sounded really good (acoustic strummed guitar, however, was awful compared to the post megavoice era), but the old drums and bass were punchy like a Korg!
And since it was before the Tyros era, guess what? the s550 *should* have seamless sound switching (which was actually on pretty much all keyboards up until the early 2000s). But yeah if it breaks down, good luck finding parts.
Mark