Advertising for Tesla at this point is fairly easy and inexpensive. For most other companies, when designing marketing tactics you need to know where in the marketing funnel your target audience is. For Tesla, it's all about the top of the funnel - generate Awareness. To your point, since there's no real competition, all Tesla needs to get across is the features of their products; no sob story, patriotism, or call to action needed. Furthermore, there's no complexity for dealership ad vs brand ad. They could potentially run the same campaigns across multiple target locations. Perhaps one campaign on the range and charging infrastructure, one campaign on cost of ownership including tax credits and price cuts, one on power and safety, one on the entertainment system, etc.
Their ads can be very streamlined, just like their production. When you streamline your ads, you can reach a larger audience and generate more sales for the same dollars spent. I would expect Tesla's ROAS to be at least twice as high as auto industry average, if not potentially 5-10 times as high, at least at the beginning. We just don't know if we don't spend.
The only caution I have is that without some sort of inventory build-up or density of stores, Tesla may not be able to take full advantage of an advertising campaign. Impulses are usually short-lived. If someone gets excited about a Tesla from an ad, they want to get their hands on one tomorrow. If there aren't enough units available for purchase or at least for a test drive, the excitement may fizzle out. Sometimes you do become a victim of your own success. It would be wise for Tesla to test the water before going all-in on ads.