Longtime reader ... first time poster.
When I first read about the trade, I shook my head and figured here we go again. The Twins trade their best tradeable asset for one minor leaguer. After I started reading about, Meyer, I changed my mind.
I think Ryan's quote in the strib article sums it all up:
"These guys are hard to get, and if you are going to get them, it's going to be in the low-to-mid minors. Once they get up to Double A or Triple A, they are almost impossible to get." (http://www.startribune.com/sports/twins/181434491.html)
We all knew we weren't going to get an ace or number 2 for Span in the majors, AAA, or AA. The best we could hope for might be a number 4. TR had to go to high A to get the best pitcher he could for Span.
I'm glad we didn't use Span and other prospects to get Shields. Why waste Span and currency (prospects such as Rozario, Hicks, etc.) in our minor league system for 2 years of Shields before he commands top dollar to stay and further hurt payroll? Rolling the dice on Meyer is the way to go. No guarantees he'll be good, but the Twins at least gave themselves a chance at a strong pitcher by bringing him in.
I'd rather have taken Meyer (I'll say "B" level prospect) then hope for two C prospects or a C and a few D prospects in return for Span. The Twins probably could have taken a quantity of lesser prospects, but they sacrificed more pieces coming back for quality. They put all their Span eggs in one basket for Meyer, but he has the best chance at producing vs. any other number of lesser prospects the Nats may have agreed to send.
I think it's silly fans (especially on the strib) are ripping the Twins for the move (the early replies of what I read). They don't understand baseball and how valuable young pitching is. You don't just buy young pitchers for 3 million like you do NBA draft picks. You need to either hit them right on the draft or trade impact players away to get the prospects. Span brought us the best pitcher he could. I'm satisfied based on Meyer's potential alone. Let's hope he's blessed enough to avoid Tommy John and cash in for a long MLB career with the Twins!

