New Road bike or New wheels?

Hi, I've got a knackered rear wheel and looking at getting either some Scribe's or perhaps some from cycleclinic/wheelsmiths - for under £400 (do like deep section rims though).

My quandary is my bike is a Mango Point AR which cost £600 - Am i mad thinking of buying wheels for £400 on a £600 bike? Its basic spec Claris and is heavy.

I've gotten into road riding more than I thought i would (longtime mtb'er) and the Mango is my first roadie bike so in the future probably would want to upgrade to something better - like a ribble r872 disc or similar.