Considering Tesla has said many initial Model S owners "sold" 4-5 Model S, with some being responsible for "selling" 10+ this promotion makes a lot of sense. This sounds like a great way to raise brand awareness, and to increase the enthusiasm among owners. Many owners probably know 10+ people who can afford to buy a Model S or X, many of whom probably would do so after a "test drive" This will encourage many early adopters, including people who want the exclusive Founders series that will likely be worth $150,000+ to show their friends and family how awesome the Model S and Model X are.
There is no need for the people to "convince" anyone The Model S or Model X is a vehicle worth buying. The Model S basically sells itself. This is a win win for those who are very enthusiastic about showing the Model S to their friends and family, and are involved in the Tesla community.
This isn't advertising in the traditional sense, and Tesla isn't paying anyone to do anything. Tesla is simply encouraging and rewarding Tesla owners for something many already do, and is encouraging owners those who are simply owners, to become more involved in the Tesla community. Tesla is seeing demand for around 60,000 Model S annually without any discounts, advertising, or marketing gimmicks. This could have a very significant effect on Model S and Model X sales.
This is also encourages Tesla owners in states/countries where Tesla can't or doesn't currently offer Test drives to become "Tesla Ambassadors "of sorts, and let their friends and family exprience first hand the reason(s) they bought a Tesla.
Also, this is a temporary promotion that in my opinion is more about seeing how high demand can go, without any direct effort by Tesla to sell vehicles (aside from Test Drive events) prior to the Gigafactory being opened, to have a measure for how high Tesla should aim to make the initial output. (Maybe also to convince suppliers and investors to help speed things up?)
Also, who doesn't want a "golden ticket" to attend the grand opening of the Gigafactory? Anyone who receives the "golden ticket" will be a Tesla customer for life.