I don't get how on the earth can using CVS for version control be an appropriate reason to consider a software project bad. Yes, CVS is old and centralised, but, is it that big of a deal that it's usage by a project per se projects the project old and inactive?
However, I don't think you should ever avoid writing something you'd enjoy for the sole reason that there are prior attempts (successful or unsuccessful). If you aren't motivated by money, you won't lose anything if your project doesn't get a single user, but you will always gain enlightenment and great experience.
CVS still works just as well as it ever did, but it is super crusty at this point. If an open source project hasn't transitioned off of it, that's a sign to me that the maintainer either doesn't know any modern DVCSes, or doesn't care about the project enough to transition to them.
It's not a guarantee that the project is dead or outdated, but it's a smell.
Of course, I consider still being hosted on Sourceforge to also be a smell.
My point is that the argument for CVS is probably just a forced, faulty rationalization by the author so he/she can justify writing a new implementation. But I'm repeating again that there is nothing wrong in reimplementing something just for the sake of it—you have nothing to lose and a lot to gain :)