What range would make you plug in less or not at all?

I suspect the Tesla PowerWall is mostly Tesla in name only. It is a way of reaching out to more residential customers for SolarCity, which already installs PV and battery back ups for commercial use.

Sounds like the salesman was trying to push you into ordering a PV system now instead of waiting for the PowerWall, and/or he was poorly trained on the system's purpose. The PowerWall site stresses shifting solar power use more than basic time shifting for off peak rates, and SolarCity's site focuses more on the back up aspect.
Backup Power Supply – Home Battery Backup System – SolarCity

 

Then why send a SolarCity employee to push a PV system a person doesn't want?

The goal of the Gigafactory is produce batteries at long enough cost to make affordable, long range BEVs possible. Expanding battery sales to non-cars also helps with that, but Tesla isn't planning on entering the PowerWall business like they did the car one. At the bottom of the PowerWall site, they are asking for distribution partners.

 

I'm sure it is, but the companies actually putting iPhones together aren't named Apple.

SolarCity and Tesla are linked.
Tesla needs cheap batteries in order to make affordable long range BEVs possible. Selling batteries for other purposes helps that. Packing those batteries into a ready made home back up/time shifting unit may even be a better plan to do so. SolarCity already installs batteries for time shifting for businesses and even governments. Using them saves Tesla to resources of building their own distribution and retail network. likewise, SolarCity will probably get a batteries that they use for their current business for a better price from Tesla.

The PowerWall doesn't come with an AC-DC inverter, and Tesla would probably like you to buy it from SolarEdge or Fronius. The PowerWall and Tesla Energy are simply not a Tesla only thing. Press Kit | Tesla Motors

 

yes, "anti-islanding" is the industry jargon for wind/pv inverters / battery backup inverters that require grid input. I too have not been able to determine from their website whether or not such capabilities will be part of Tesla's power wall. It'd seem to make sense they do, or what'd be their advantage?
Anyway I've read extensively on 'spoofing' our sunpower anti-islanding inverters, and purchased a surplus cell cite battery backup bank (includes 240v DC/AC inverter) for that very purpose - proof of concept. Long stort short, these inverters aren't so much needing to see 100 or 200 amps of 240v, surprisingly, as much they're looking for a pure 60htz sin wave that they need to sync with. As a prudent electrical hack, I quit messing with it before I fried myself.
I think what's more important is the kind of battle on the horizon from the utility companies, as such devices can quickly wreck their business model.

i smell kickbacks

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I thought about using a small inverter to "fool" the PV inverter (I have a PowerOne/ABB PVI-6000), but everything I've read suggests that all that will happen is I'll fry the small inverter and possibly the ABB unit, so I'll pass on testing the theory.

Clearly, the utilities do have a concern - unless there's a failsafe way to isolate PV inverter output off the grid so that a lineman working on a "dead" line doesn't get a nasty surprise.