The 4 and 5 spots in the rotation shouldn't be locked down by people making 8 figure salaries. As it is those positions are only open because of injuries to Lackey and Daisuke who are walking violations to that cardinal rule. Those spots should be held open for viable young pitching, but since we haven't seen a young pitcher we haven't wanted to trade for one last feeble grasp at the Series at any point in the last 5 years that's going to be a problem.
Frankly, Lester, Beckett and Buchholz should be a good enough top 3 to keep us relevant even if we have trouble filling the bottom 2 spots anyhow. But since Lackey and Daisuke are eating the money you need for your bottom 2 rotation spots without returning any significant value, I'm not sure what you expect them to do.
Realistically what the team should do, from purely a roster standpoint, is punt for multiple seasons, start letting some contracts run out and trying to improve their batting average at the draft. This team has been running the roster like it's one big piece away from another Series ever since 2007, and it's not sustainable. You can see the signs of wear pretty easily in the farm system right now, looking around at just how little high end talent we have in the upper minors anymore. What little we have always goes out to finding that one last piece, so it'll never get any better either. And we all pretend that we can afford to part with any one prospect because it's just a rookie after all, meanwhile we once again sign expensive veterans to fill that spot and bog down the roster even further.
This will not get better until we accept the fact that we have an aging core and need to rebuild it. It's that or continue to delude ourselves year after year and wait until the crash comes in earnest, and wind up where the Mets are, or even worse, where the Astros are.
We need to pull back for awhile, possibly as much as half a decade or more, and really rebuild the team from the ground up. It won't happen though. Too much money at stake.