There are tons of threads on wheel upgrades. And tons of questions to ask and lots of opinions, so there's no easy answer. That said, here's my experience in the last 12 months:

I upgraded my 2013 Roubaix from the stock DT Axis 1.0 wheels to Mavic Ksyrium Elite S last July and am very satisfied. These cost $800 or so. In addition to the weight savings (which has a big effect on a rotating mass), these wheels appear to have better hubs/bearings and are pretty durable.

I recently upgraded my wife's Ruby from Mavic CX22's to a set of Boyd Roleurs and although she's only been on them for a short time, she's really happy. In her case, we dropped about 1.4 lbs in total for the wheelset. The Roleur's were $400+shipping.

Some good advice I received from an experienced road-rider: Regardless of what wheelset you choose, it's a good idea to try and buy them through your LBS. It'll further develop your relationship with them and they'll have some "skin in the game" in case you need help with repairs and/or truing sometime later on.

Hope this helps.