Well if you are happy with the quality you get from your current camcorder then there really is no need to replace it. You would get better quality from a DV cam, but more than likely it would be poor for indoor use without additional lighting.
So what are your options?
Basically you want to ignore the USB ports as although you can get analogue devices that will connect via USB they are often low quaity and can cause lip sync errors.
The best way to connect an analogue converter to a PC/laptop is via firewire. Even on a laptop you can add a firewire port for around £20-£30(ish!). I would then advise one of the Canopus ADVC converters. They have differing features where some can convert back to analogue where some can't etc. Do a bit of reasurch to find out if you want any of the additional features, but they can all be bought from
www.sirentechnology.co.uk amoungst other places.
ADVC100 - £193.88 (A/D & D/A)
ADVC55 - £151.58 (A/D only)
ADVC300 - £410.08 (A/D & D/A and has TBC that will help to improve the PQ by a fair amount)
I have never used these devices as I have onboard analogue & digital inputs on my PC capture card. But everybody that has reported on these seems to be very happy with the results.
Mark.