I have Home Studio 2002 and Sonar 2.2XL. If you only need to record 1 track at a time then I don't really see the need to upgrade. The main reason I got Sonar is I am a drummer and only being able to record 2 tracks at once is a real pain, and kinda wasn't really useful with a C Port.
In HS2002 you can get latency really low if you have a decent sound card, and you can still use DXi synths and effect plugins. I would upgrade you're computer before anything else, just like HogansHiro said.