That would be a pretty dick move. "You gave us a ton of money buying a ridiculously expensive car, and as your reward you have to wait longer than people who we've never even seen before."
I could see just not giving priority. As it is, they're rewarding customer loyalty, which is a pretty common thing to do.
Well, either rich people want "the affordable one" or they don't. If they do, why not reward their loyalty? If they don't, then it doesn't affect anything.
In any case, I don't think it'll be a major factor. All current owners already have a car, after all. How many need another one? Out of ~120,000 current owners, how many head-of-line orders will that translate into? I'd think it would just be a couple thousand, which won't make a particularly big difference in the timeline for others.
I could see just not giving priority. As it is, they're rewarding customer loyalty, which is a pretty common thing to do.