Martin was absolutely having the best season among the relievers we acquired, so it's likely that his market was pretty hot, driving up his price. Also, Allard was/is a 45 FV prospect. A 45 FV prospect for a rental reliever having a great season isn't exactly a huge overpay. And as previously stated, it seems Allard simply had fallen pecking order among our prospects. Making room on the 40 man was also a consideration as well.
Seems like a big nothing burger we're discussing here. Allard's ceiling is pretty limited anyways. Maybe he reaches John Danks territory at his highest if he develops more. But more likely, he's another Paul Maholm/Chris Capuano type of pitcher if he can remain healthy. Durable 5th starters do have value, but it's something I would never really lament giving up. Much like I don't lament giving up Jason Marquis.
Side note: It's nothing sort of amazing that Jason Marquis has 124 career wins and only 6.8 career bWAR (8.8 fWAR). For reference, Ted Lilly played over the same time frame as Marquis and had only 6 more wins while having over 20 more career WAR.