That, "SOME DAY" it might be more economical to install an identical system does not change the fact that it's still a silly splurge NOW.
If the system does NOT pay for itself over a reasonable period of time (and within the lifetime of the product warranty), you're splurging. Not spending wisely.
I pay close to $250/month for power (it just went up 47% in CT in the last 6 months for the same power usage). So if the 10kWh PowerWall costs me $3,500 (+inverter, grid tie-in, installation), then it pays for itself in ~18 months. That's a pretty easy sell from my perspective.
Adding $10k of solar panels to the system to go completely off the grid, just adds to that value, and to the resale price of my house if I choose to sell it within the next 10-20 years. As panel efficiencies improve, I can upgrade those panels, or add an additional PowerWall, and increase that independence.
Totally worth it, in my opinion.
Besides, many (most?) communities are now putting a quota on the number of solar installations, because of the pressure they put on the common utility/grid system (yes, they do -add- more pressure to the grid, contrary to common thought, especially at nighttime and when there is heavy, localized cloudcover), so if you wait, you may find yourself the only one on the block who can't add solar because it's prohibited. A PowerWall tied to the common utility can relieve some of that pressure, and increase the independence from a constant feed from the power company.