First of all, let me say I am a big Murphy fan so I don't take this lightly.  

While listening to MLBN this morning on the drive in, a Cards fan was fed up with Jay, Freese and Lynn, oh to have their problems but I digress.  Obviously as a Mets fan I would take Lynn in a heartbeat as well but I can't see them trading him unless it's in a package to get a true SS so lets focus on Jay. 

Jay 3-15-85 .296 .356 .400 .757 109 1.2 2.5 3.7 1.9
Murphy 4-1-85 .290 .333 .424 .757 108 1 2.8 1.3 3.0

Amazing the similarities.  Murphy will be more expensive than Jay by one year as Jay is first time arbitration eligible and Murphy is in his 2nd year. 

There's no doubt that the Cards are concerned about 3B, Murphy's natural position.  Freese while only 30 isn't looking like a guy who will age well.  The Cards also seem to value versatility and having a guy like Murphy who could play 3rd, 2nd and 1st would most likely interest them.  Jay also could be the odd man out as star prospect Oscar Taveras has been doing more than knocking on the door (although his season was cut short due to ankle surgery)

For the Mets Jay would provide another answer in the OF with a guy who has been known as a very solid fielder to say the least.  While errors aren't the best way to judge an OF, he has a career .995 Fld% and has committed 5 errors in 3869+ innings, yeah you read that right, he's committed 1 error in the last 2 years.  With the Mets expanses in the OF they could play either he or Lagares in CF and RF and then find a slugger for LF which is usually much easier to find than a RF slugger.  

Imagine the defensive OF of something like the prize candidate of some Granderson in LF, Lagares in CF and Jay in RF.  Pitching and defense anyone? 

Again, it isn't often that a trade seems to make complete sense for both teams but to me this is one of them.