What features are you looking for that you feel is missing from Vista Home Basic?
If you dont know exactly what you hope to gain by upgrading, and just feel it would be a good thing to do, then dont bother.
Home Basic lacks the Media Centre, and I dont think it can work with an XBox, and there are a few other things, but probably nothing you could not gain by downloading a free utility from the web.
While I always say to people go for Home Premium over Home Basic on a new PC, I dont think it is worth the cost to upgrade, and for a home user I dont think it is worth upgrading to Ultimate anyway.
Here is a compariosn list that Microsoft put together
http://www.microsoft.com/windows/windows-vista /compare-editions/default.aspx