It does have good logistical value. It's the center of the Galactic economy and one of its primary sources of eezo. Any resources that can be pulled off their to assist with the crucible would be very useful.
Because Shepard spending the entire game trying to get the other races to send their fleets to the Sol System is stupid. Thessia is described as a "vital military asset" in the N7 minigame. Thessia ensures that the galaxy's supply of eezo is maintained during the war. Both Palaven and Thessia had greater strategic significance than Earth.
Sure, Thessia is an important asset, but not important enough to divert entire fleets that are needed elsewhere to its defense. If the Reapers have already beaten the planet's defensive fleets and forces, then it's too late anyway.
I also think that gathering fleets to retake Earth is stupid, but it at least makes sense when the Reapers(for whatever reason) take the Citadel to Earth.