If I buy the

Watch, it won't be to impress anyone, except myself. Also, I don't really care for gold jewelry. So, at $5000, I wouldn't be interested in the gold option. At $500, I still wouldn't be interested (assuming the internals are the same).
One thing is clear, though. The

Watch is a new direction for Apple. Are they going follow the path that they have with the Mac Pro, where they release a new one every year and expect at least half of their owners to upgrade? Or will they do something more like they've done with the iPhone, where customers buy one and expect it to be expandable and to last many, many years?
Oh, wait. I think I got that backwards.
Perhaps the

Watch will be something you can take to your

-authorized jeweler every couple of years to have the back removed and the insides replaced, giving you a new battery, new and better sensors, new processors, new antennas (LTE, GPS), a new display, and even a new crystal if you need one, all for a few hundred bucks. (Some of the bands they sell will cost more than that!)
It won't make sense to replace the innards of the Aluminum model, and it may not even be possible/supported. If you want a new entry-level

Watch, just put your four bills on the counter (virtually, of course) and you're good to go. But for the higher end models (we could see platinum and titanium, too), it's conceivable.
I don't have any inside knowledge, so this is just my musing, but there's no reason Apple has to repeat what it's done with the Mac Pro--I mean the iPhone. Just because they've
always done things one way (when you ignore the times when they didn't) doesn't mean they have to do it that way in the future.