Now that we've seen two teams more or less acquire Cliff Lee at the same time it's easy to see the Cardinals shouldn't have wanted in on it.
↵The trade that wasn't tracks better with what the Cardinals could have offered than the one the Rangers eventually made, so let's use it as an object lesson. It seemed set when the Yankees agreed to send superprospect Jesus Montero to the Mariners as first chair in the deal. Montero's a better prospect than Shelby Miller, if similarly uncertain. In 2009 he had an outstanding season as a 19 year-old split the pitcher-friendly Florida State League (high-A) and the AA Eastern League; all together he hit .337/.389/.562, with 25 doubles and 17 home runs. His 2010 has been slower, but as a 20 year-old in the relatively neutral International League (AAA), .256/.329/.408 is still really impressive.
↵He's a catcher who'll probably end up at first base, but his bat will play anywhere; he's one of the top ten prospects in baseball. And that's just the first part of the deal. So throw Shelby Miller into the deal; because he's no Montero, and the Mariners were, at the time, desperate for a catcher, toss in Bryan Anderson, the Cardinals' line drive-hitting Memphis understudy, and hope you can sneak Matt Pagnozzi on the plane to Seattle instead.
↵Next up, the Yankees planned on trading 2B David Adams and pitcher Zach McAllister. Adams is a hard-hitting second baseman who doesn't have much in the way of tools but consistently outperforms them. As a rough comparison, imagine the Cardinals throwing in 2B prospect Daniel Descalso—McAllister has been a better hitter, but Descalso is perhaps more likely to stick at second. McAllister is a high school pick who's reached AAA, bizarrely enough, as a polish guy—good command, low strikeout rate, sinker. Lance Lynn is better, so that makes up for the difference between Adams and Descalso.
↵So in exchange for almost getting Cliff Lee, the Cardinals could have traded their first, third, and ninth best prospects, as well as the guy who by all rights should be backing up Yadier Molina while he struggles to hit. In exchange for three to four months of Cliff Lee, they could trade six years of Lance Lynn and Shelby Miller in a rotation that won't bankrupt the club.