Normally, I'd agree with you, but in the international market, quality is pretty fungible--the distance for these guys from the major is immense, and rarely do prospects like Sano emerge as such obvious quality investments. Given the higher risk, it does make more sense to spread out that risk over many players rather than a few.
Another fact about quality and quantity: there are 30 teams, so by definition there will be teams that don't sign a "Top 25" guy. The Twins have signed one or more such high-ceiling prospect in each of the past several years, so no one can legitimately complain that they don't get their share of "quality". The record clearly shows that they get both quality AND quantity. You might put Arcia and Santana in the "quantity" category, and Polanco and Thorpe in the "quality" category, for example.
Nice to see the Twins continue to be aggressive in the international market. They're getting terrific results.