As long as what you are doing is working OK... you should be fine.
It's been our experience, helping lots of people through the years, (6+years for me) that the USB mics are problematic for most of them. The big issue is that the USB mic is seen by the computer as a sound card, which it is. Since it has no speaker output, your computer has to use 2 different sound cards at the same time. Quite often, those 2 sound cards have clocks in them that do not sync up and there are cases where the tracks start to drift apart as the song progresses. In addition, the factory card used to play the music gets overloaded when synths are introduced and you start getting dropped notes, clicks, pops, latency, and even complete audio engine failures in the middle of the music. I'm not saying these thing will happen, just that they are likely to happen at some point the further you get into recording. Projects get bigger, you throw in a few synths, and before long, you run into these symptoms.
If you start to experience trouble with the USB mic, check here:
http://forum.cakewalk.com/Guide-SONAR-usb-mic-Samson-C01u-or-C03u-mic-m1618556.aspx The info might be useful to you. The other option is to upgrade the gear to an interface & condenser mic. I have never had issues with latency, pops, drops, since I have been running my interface. I can run projects with 20+ tracks, and multiple synths without a single hiccup. Some folks here have reported running 80+ tracks in a similar manner with no issues..... because the sound card/interface can handle the job.
So... in short, as long as what you have is working, keep going. No reason to buy anything you may not need. If you encounter issues, you also now know the solution.
BTW: post your music in the songs forum when you get some ready. I'd love to hear what you are doing.