JAIQUAWN JARRETT should be exhausted after tonight's game.

So should Casey Matthews.

And Mike Kafka.

They all should play. Actually, they all should start.

Really, why not?

At 4-7, the Eagles' season is lost.

Still, the team can salvage something precious: information.

Andy Reid, with 2 years and $10 million left on his contract, will return. He will not quit, because he knows how good his team can be with a little bit of spit and polish.

So he needs to know what he has when he tweaks the roster come spring.

Jarrett is a second-round rookie safety out of Temple, a draft-pick investment too precious to waste on the sideline watching Nate Allen limp and hitch through the last five games. Allen's titillating promise from last season evaporated when his right knee collapsed against the Giants last December.

The joint cost him the first three starts of this season. Allen clearly has not fully recovered, nor should he be expected to be fully recovered. It takes at least a full season to regain the strength in a joint repaired the way his was.

So Jarrett, who can play both safety positions, should start. Tonight. There will not be a dropoff - not if Allen's play of late is any indicator.

Matthews, a fourth-rounder, displayed early this season that he could not effectively play either middle or outside linebacker. Not without a full offseason to prepare. Matthews was asked not only to play middle linebacker but also to run a defense that was new to all of the returning defenders. So, you have a rookie calling the shots for veterans who would not know if he was wrong.

The Birds pushed Matthews to the team's fringe after three starts. Now, 2 months later, it's time to see what he has learned. Throw him back in there with rookie Brian Rolle and Jamar Chaney. Akeem Jordan, a fifth-year special-teamer, has done little to justify the first-team status that fell to him the past 3 weeks, and he'll be long gone in 2012.

So will Vince Young.

Kafka will not.

That's the main reason Kafka should get the snaps tonight. Young is on a 1-year deal aimed at salvaging his image and his talents after a bizarre and, at times, absurd run in Tennessee.

Kafka will not start tonight - on a short week, Young ran with the 1's at practice and will replace Michael Vick for the third straight game - but Kafka should.

In the blowout loss to the Patriots on Sunday, Young proved, once and for all, he is not an NFL passer. He didn't hit a single receiver in stride or on time - his bugaboo during his 5 years in Tennessee. He threw for 400 yards, but he was just 26-for-48.

He has had 4 months of tutelage under quarterback geniuses Marty Mornhinweg, Doug Pederson and Reid, who remade Vick. He remains the same passer who hesitates, who flicks up sandlot, sidearm lollipops.

He will show more of the same tonight. He engineered one significant drive to beat the listless Giants. He threw a lovely bomb to Riley Cooper to begin Sunday's game. He then failed to execute for the next 30 minutes. More than half of his 400 yards came after the Patriots had the game in the bag.

His fourth interception in two starts helped squash the Eagles' chances. His touchdown pass came so late he probably should not have been playing. Tom Brady wasn't.

Hopefully, if things get out of hand against the Seahawks, Young will not be left in. Even if things are close late, and if Young has not been sharp, Kafka deserves a shot . . . and the Eagles need to know.

Can he be a viable backup?

Only game experience will tell.

There are other, less pressing positions to plumb.

Dion Lewis, the fifth-round rookie understudy of feature back LeSean McCoy, should carry the rock every time McCoy does not. McCoy has a sprained toe.

So, no more Chad Hall. Please.

For that matter, as soon as the season is finished mathematically, McCoy should be shelved. Running backs have only so many car crashes in them; ask Robert Smith or Tiki Barber.

McCoy also should have his contract extended. In his third season, he wants a new deal. He deserves it.

Certainly, McCoy has done more to deserve it this season than prima donna receiver DeSean Jackson, lately chronically tardy and timid.

For that matter, when the season officially becomes meaningless, Jackson shouldn't be playing, either. To what end?

If Jackson does return to the Eagles, via franchise tag or contract extension, better to ensure he doesn't get hurt in meaningless games. If the Eagles tag and trade Jackson, as seems likely, he will not be damaged goods.

While they're at it, how about more Clay Harbor? He runs like a receiver. A fourth-round pick in 2010, part of a spectacular draft class of tight ends, Harbor has blossomed this season. As a seasoned bookend with Brent Celek, the pair could be devastating.

Finally, when Dominique Rodgers-Cromartie's ankle heals, just bench Nnamdi Asomugha. Not punitively but protectively. The Birds have to know if DRC can cover at all, since he failed so convincingly as a nickel corner. DRC went to the Pro Bowl covering receivers on the outside. Asomugha, the jewel of the offseason spending spree, is fighting a sprained knee.

Sadly, none of this will happen tonight.

The Eagles have a chance . . . the chance embodied by the Seahawks, who last season went to the playoffs and won a game with a 7-9 regular-season record.

That is not going to happen again.

Better to watch and learn.

Send email to hayesm@phillynews.com