However, it's also possible they build their spaceships like we build cars--not well enough to last over a decade (although my dad's work van begs to differ :P). If they've had the technology for space travel for thousands and thousands of years, chances are they can make spacecraft fairly cheaply. Larger ships, like Star Destroyers, would definitely be built to last longer, however.
Alternatively, spaceships are actually expensive in the Star Wars universe and they are built to last, as you think should be the case.