If you have a recentish Roubaix then you probably have DT Swiss rims, which I thought are considered solid if mediocre. Did you ride them under any harsh conditions?
You can pay however much you want for wheels and it would be fine, b/c a lot of cheaper bikes (cheap in this case just comparing to the Roubaix lineup) are cheap because the wheels are nothing special. Specialized doesn't put good wheels on until the Expert or Pro levels.
$600 would be ballpark of where you start to have options better (significantly lighter or significantly more aero or a compromise between the two) than what you had, hand-built alloy from sites like ProWheelBuilder and Hunt, or even Chinese carbon rims with cheaper hubs like Light Bicycle or the more well-known vendors selling on eBay and Amazon.
$1,000 would be significantly better (lighter and more aero) from Light Bicycle and the like. $2000 and up gets you arguably only a small upgrade over those other than bling factor.
$300ish would get you something more reliable but not faster (maybe even heavier), from any of the big Internet bike store sites. People seem to vouch for wheels from Shimano, Fulcrum, and the like. Nothing wrong with a mostly lateral purchase other than redundancy when you get your warranty replacement. When it comes to wheels, if you're financially comfortable with spending more, I think you should.