What you're suggesting is what I'm already doing and it doesn't take a $20,000 Media Composer Adrenaline setup to do it. The main benefits of professional hardware are usually A) more inputs and outputs and B) easier to use "all in one" software packages and C) real time video effects. Since I only need one input, and using a number of freeware programs actually gives me more flexibility than working entirely within media composer, and i'm not adding any video effects, that kind of rules out any reason to spend more than $50 on a capture card.
Or $6000 on a fully loaded Final Cut
(we used to be all Avid). It made me a little nervous seeing some posts about digitizing through a DV input, etc. It's awesome that you're on top of the technical.