any degree is not a vain....you r doing two of the most prestigious courses in commerce and u shud be proud of it...ofcourse CA + CS is a jhakkas combo (pardon my language) but CA+ICWA is not bad either...you could complete both together, i m sure it will fetch you very good opportunities both in terms of job satisfaction and monetary packages., look at it this way, you could be both a financial and cost accountant. So, dont worry u r doing the right thing...never think anything is vain...every degree has got its importance, only thing is some courses carry pride and prestige which the CROWN 3(CA,CS,ICWA) carry.
once you complete both you could do CS too slowly. CWA's are given exemptions and once u have experience u r exempted frm the training too. so..best of luck