One question, though. How much do you value the dealer's warranty? Equivalent to $?/year?
How can you put a price on peace of mind?
Generally speaking, though it's not really the warranty that is the difference, it's the fact you are getting a brand-spanking new piano that will (presumably) not need much work other than a couple of tunings a year and regular maintenance until a few years down road.
When you're buying used, and something 30 years old, not only does it lack a warranty, but it will most likely need a lot of work to bring it up to a level of playability and enjoyment. Now, if the previous owner has done all this work (and can provide receipts showing what they've done to it) then perhaps it's a good deal. Still, 30 years for a 5'1 baby grand is pretty old. At that point some major repairs may be needed.
Have you have a piano tech check it out? That will really give you an idea of what repairs are needed.