Loaded economy cars doesn't make sense in the first place, due to the obvious that you've already noticed : it brings you into the range of cars that are dominantly superior, like the '11 Stang V6.
The current Sentra is pretty underwhelming. The CVT, just like the one in the Rogue, is not a winner. The 5-speed in both the Focus and the Sentra is pretty good though. The real fail with the Sentra is the weight and handling. It feels heavier than the Altima, and the rear suspension is something called Torsion beam axle, and it's just total ass. It's okay for puttering around town, but it's garbage when you compare it to Civic, Focus, even the Corolla.
I expect Nissan might significantly update the Sentra next-gen, who knows. Next-gen Civic should be here soon as well.
I have a Focus Coupe (08), and I deliberately got the lightest/simplest/cheapest one I could find. The drivetrain doesn't get any better with the SE/SES, the stock stereo is pretty good (ipod jack + mp3 playback), I don't need NAV, I don't like cheap leather, and power windows/locks seem almost pointless on a compact coupe. About the only thing I would have liked in the options was the moonroof, but I'd probably rarely use that.