In my experience, people who use the phrase "ridiculously overpriced" are always outside of the target demographic.
Every business hopes to make a lot of money. As for "taking advantage of rich people," that's what premium segments in EVERY market are for. The marginal value of money is less for wealthy people, and the trick is to figure out if the marginal difference in product quality outweighs the cost for that target demographic. In some product categories, there isn't much of a premium segment, because rich people simply don't care if the product is premium or not. But in many others, including clothing and sporting goods, wealthy people are often willing to pay a lot more for goods that are only slightly better. (In fact, some luxury markets are actually winner-take-all, where the absolute best product has very little elasticity of demand because for some people, the value of the product is the knowledge that it is "the best." Think of Birkin bags, for example.)
I'm not sure that Trackmith has the winning formula, and there are problems with trying to come up with a premium running brand. For example, we don't have the same style heritage to draw on that Rapha did with cycling. Another problem is that running clothing is so simple that even when cost is no object, it's hard to make something that's clearly "better" than your generic Nike stuff. Nevertheless, runners are a large and very wealthy demographic, and it's awfully surprising that a premium running brand hasn't emerged before now. Lululemon has tried, as did Brooks with the recent Pure Project.
I'm not sure that companies like Trackmith will help the sport either, but it's possible. Nike was an undeniably cool brand in the 70s and early 80s, and it was very much associated with running. That association made running cool. Under Armour has made football cool(er) as well, even though football didn't need much help.
If all you're saying is that Trackmith will fail, you may be right, but not for the reasons you suggest. There are lots of people who can afford their products. I for one would have no problem spending $65 on a pair of shorts if they were really excellent. They last a long time, and I spend a lot of my life running, so it's not really that big of an investment. Less than the cost of a decent round of golf. I think the real test is whether they can deliver the goods. If the gear is really excellent, both functionally and stylistically, then they'll do very well.