There are potentially two option here;
1) The ship is not obsolete. It remains the acme.
Your assumption here is that technology is still advancing and that when they return home, the ship will have been superseded by more advanced technology. The flipside of that is that it's certainly not beyond the realms of reality to imagine that this ship is already capable of transporting the maximum number of people at the maximum possible speed.
With a self-repairing, self-cleaning and apparently infallible ship (note that this is the first time that a sleeper unit has ever broken down), presumably all that needs to be done when it arrives home is to refuel/restock it, replace any broken components, give the crew a few weeks furlough and then send them straight back out again.
Passengers: Original Screenplay
2) Bits of the ship are obsolete
In the event that technology has moved on, the ship appears to be modular in construction. Jim is able to replace the entire computer core simply by taking the broken part out and slotting in a new one.
Again, it's certainly feasible that the ship has received multiple upgrades over its lifetime with the main living areas simply being the bits they've kept while upgrading everything else. In the original script Gus states that he's made multiple trips on the
Excelsior Avalon and just lives wherever they land it until it's ready to fly again.