I can understand your qualm about Minaya exceeding his stay. But that's on the ownership.
As for Sandy, if you add up things that the ownership wanted from him:
1. Reduce payroll - Check
2. Don't spend any money - Check
3. Acquire enough talent through drafts and trades to keep the team afloat - Check
4. Stabilize the organization after the whole scam - Check
5. Keep most of the fans remotely interested - Check
The deliverable s for Minaya and Sandy were completely different. Minaya made the splash and dash signings to put the Mets back on the map. It back fired in 2008 and 2009 and Sandy was hired to do the above things.
The cutting of Castillo, Bay was probably a PR move that Sandy convinced the Wilpon's. It helped save some face. The signing of Wheeler and D'Arnaud has helped in maintaining some fan interest.
It would be extremely hard for a GM to go above and beyond the call of duty, when he knows that there is no money to spend and he can't even justify to the owners on signing a draft pick over slot money.