Ethnic stores are not solely for that specific ethnic population. Consider an ethnic store a very cheap trip to an exotic locale.
There are two Russian stores right near me; I patronize one more than the other. The store carries more than just Russian products; it carries produce, cheeses and meats from all around the world (obviously, not for the kosher consumer), and an incredible variety of packaged products from many European countries (predominantly Eastern European and former Soviet republics), as well as products from Israel. There are candies, canned vegetables, wines and beers, teas and coffees, desserts, breads and jams, rices, beans, sauces, frozen foods, dairy products, etc. - the list goes on and on. It offers baked goods, freshly-prepared take-out foods, and fish and fish products. It also has health and beauty aids, vitamins, herbs and supplements, and a huge variety of souvenirs from various countries. All in a rather small space.
But what is critical here is the price point. Generally the produce, nuts, dried beans, and rices are much cheaper than what is found in a grocery store, and the variety of offerings can't be beat. I know to visit this store first for produce before I go to a grocery store, because I know that my bill will be lower. And that definitely helps in the frugality department, without sacrificing quality.
There are many other ethnic stores out there: Middle Eastern, Indian, Asian (Chinese, Japanese, etc.), Hispanic, and more. Take a walk on the wild side and visit another land without whipping out your passport!
(wow that was incredibly cheesy, but it seemed like such a fitting way to end the post...)