Well my bass boat will do everything a new one will. It belonged to a local physician who used it only a few times. It is in perfect condition, but you never know when something will need repair.
On the other hand, a new keyboard will often offer improvements and features that older ones don't. If it ever comes down to it, I would sell the boat to buy a new KB in a second! As I said, it's a matter of priorities. The keyboard is my source of income and therefore essential.
We obviously don't NEED the latest and greatest, but I find a new one now and then keeps me interested and excited. While I become very comfortable with the various operating systems and the deep-down capabilities, I don't want to have to spend several weeks making a keyboard usable. I want to turn it on, spend a few days getting comfortable and setting it up for my purposes, and then play it. I'm sure close to half of the songs I do nightly are requests. No matter how many songs I have set up with registrations ahead of time, there are always more that I must do on the fly, while a couple wait to dance to "their" song.
When you turn the thing on the first time, drums should sound like drums, highs and lows shouldn't need much adjustment. Effects should be set at least in the ballpark. You shouldn't have to load piano samples, or any other samples, for the thing to sound like the instruments you are emulating. If it has vocal harmonizing, it should have some presets that sound pretty much like someone singing harmony with you, and shouldn't need a lot of editing. Is that asking too much?
DonM