Rick Porcello is an established major league pitcher. The Padres' rotation is in need of help. The Tigers could be in the market for relief pitching. The Padres have relievers with trade value. This seems like a potential match. And it very well could turn into a trade. I'd caution against.
The problem I see is that even with the Padres' rotation looking as mediocre as it does, Porcello doesn't appear to be the answer. He seemed to have promise back when he was a bonus baby first round pick that rocketed through the minors, but after 120 major league starts he's not that prospect anymore. He's a guy that doesn't give out many free passes, but also doesn't strike out many batters. He doesn't give up too many long balls, but he does give up a lot of hits. In fact, no one in the American League gave up more hits than Porcello did last year. That's who he is as a pitcher. There are numbers to back this up and there are numbers that try to value him.
If you look at Porcello's Fangraphs page, you'll notice that value stat of fWAR shows that he's a 2 win pitcher, close to 3 wins last year. By comparison, Edinson Volquez topped the Padres with 1.3 fWAR last season. This stat is based on another stat called FIP. FIP is a better predictor of performance than it is a stat that tells you about results. It basically keeps predicting that Porcello will get better results than he does. But, then he goes out and doesn't get those results. A more results based stat like the bWAR used on baseball-reference will show you that hasn't been worth 2 bWAR since his rookie season. His 1.4 bWAR in 2012 was behind what Luke Gregerson and Eric Stults put up for the Padres last year. Huston Street had 1.2 bWAR in 2012. In 2010 and 2011, Porcello put up 0.1 and 0.0 bWAR.
I don't like these discrepancies and I certainly don't like them at his cost. Porcello already costs as much as Clayton Richard does and that price tag will only go up in the coming years. I know fans don't want to hear about price, but the reality is that the Padres need to win by getting bang for their buck. I don't think that Porcello is that bang. I'll admit that he could be that bang, but I don't see it as likely. Especially as he gets more expensive over the next couple seasons. The Padres already pay Clayton Richard and Edinson Volquez similar salaries for not much return. It's probably not a good idea to repeat ideas that don't work.
Of course, the players involved in these Porcello rumors have salaries too. Luke Gregerson and Huston Street have been mentioned as the possible trading chits. Trading them discounts Porcello's salary and the old theory goes that you'd trade your relievers for a starter any day. I buy into that for the most part, but it just feels like this team needs the back end of their bullpen strong. Gregerson and Street are the main pieces in that bullpen. Perhaps on their own they don't provide bang for their buck (Street costs $7M and Gregerson $3.2), but as a unit the investment could pay dividends.
There's also an argument to be made that Street is near untouchable at this point. He's somewhat of a symbol. The accomplished veteran and All Star. The Closer of the Padres with a capital "C" that inherited the leadership role that Heath Bell and Trevor Hoffman had. He's one of the players the new management invested in and he's on banners in the streets of downtown San Diego. He'll be tradeable at some point, but I don't think that point is now.
Gregerson is a slightly different story. When the trade deadline roles around he's be as close to free agency as Mike Adams was when the Padres traded him to Texas. He's been both a 7th inning and an 8th inning ace, but hasn't been quite as good as he was in 2009 and 2010 and isn't as cheap as he was then. If he could return something bright and shiny, then it might be worth pulling the trigger. Is Porcello that shiny thing? You know by now I say no. And it might be moot since it doesn't seem like the Tigers want Gregerson anyway.
My inclination is to let this current rumor pass and don't fret. I might even take encouragement that the Padres will give Andrew Cashner or Tyson Ross or Anthony Bass a shot a rotation spot instead of acquiring Porcello to fill it. There's a decent chance that one of those 3 is a cheaper and more productive option than him anyway.