Why should we give a crap about retaking Omega, anyway? We've already got Aria's cooperation.
Maybe there's something other than the collector base (or wreckage thereof) on the other side of the Omega 4 relay? It'd make sense since it seems unlikely that the Reapers would set up that little hidey hole for their surviving husks in the network only after the last cycle. Odds are that's where all the leftovers end up.
For that matter, Omega itself might have something hidden away? After all it was originally a Prothean mining operation. Could it just be a coincidence that they were mining an asteroid that just so happened to be orbiting close to an impassable relay? Maybe they weren't drilling for eezo but for some lost artefact. Perhaps a reaper relic like Object Rho (also buried in an asteroid) or something from one of the races of a previous cycle.
Perhaps Bioware are planning for every major DLC to somehow tie back into and reveal a little more of the origin of the Reapers? That would certainly be interesting, and a compelling hook to get fans to part with their money.
...Or maybe Shepard just wants an excuse to stare at Aria's tits some more. She was certainly one of the more interesting characters introduced in ME2 and I wouldn't mind having her riding shotgun for a nice little adventure.