I wouldn't write off AF's words so quickly (admittedly because his and VFK's match my own, but only partly so). New vets change the hierarchy and atmosphere in the clubhouse -- who is listened to, who is regarded as deserving respect and deference from the manager, coaches, and other players? When someone comes, someone else must go and others have their playing time reduced.
SF's post suggests that trading for vets is an obligatory message-sending to players and fans that management cares about winning and believes the team has a chance. Ed Wade did that a lot when the Phillies were on the upswing, and it never helped, in part because he always seemed to trade for marginal or injured or worn out for the season relievers who, not surprisingly, didn't help the team. He similarly wouldn't trade even running-out-their-contract relievers in a 99% lost season, because he thought that sent the wrong message. Past GMs have done a lot of these message-sending acquisitions in the off-seasons of seasons they didn't expect to lead to the playoffs, going way back to one of my favorite examples: Tartabull. For these additions to actually help the team win, they need to be clearly plus additions who fill for-real holes.
When the Phillies finally won in 2008, Gillick got guys at the deadline who actually moved the needle.
I agree with AF that the needle was moved this off-season, because Middleton finally stepped in and insisted that Klentak do more than the-minimum-he-could-get-away-with-send-the-trite-message-that-we-sort-of-care acquisitions. The relievers he signed were a big yawn, injured, and not all that promising. They were pro forma, I did my job signings. Then we got Santana and Arrieta. I don't think we got them because their price fell. I think we got them because Middleton let Klentak know that he was unhappy with the off-season.
Adding even good vets doesn't always help the team. All the Phillies post-2008 additions, and RAJ made some potent additions didn't help us in the post-season. The enthusiasm and over-performance of the 2008 team was never duplicated.
The Phillies didn't do it with mirrors prior to the trade deadline. They found ways to win. Players, especially the streaky Hoskins and Herrera, took charge of games. The injury and (possibly injury-caused) swoon by Hernandez has hurt. But the post-deadline Phillies have swooned. The magic which was previously there is gone. It may yet return, but it isn't hard to say that the deadline deals at least did not help the team. Gillick had that magic touch in 2008. Haven't seen it before or since.
It would have been nice to have gotten Machado. I don't know what it would have traded. We ended up trading Kilome. Could a trade have been built around him. I still don't think the Orioles wanted the injured Crawford (and possibly not even Sixto, whom I certainly would not have dealt).