That's answered in the article. If a pitch is thrown outside, it's hard to pull but easier to hit to the opposite field. The fact that Morneau is having success hitting it the other way means that the strategy of pitching him outside and letting him chase will (hopefully) be less effective.
This would be a horrible use of money. Even if he adds 10 wins, that probably isn't enough to get this team to the playoffs. The Twins should not be inking any massive, multi-year contracts until they're actually in a position to compete, i.e. hopefully when some of their prospects in the lower leagues have developed.