I assume most people would agree that the answer to your question would depend upon lots of factors -- quality of the video, looks of the participants, ticklishness of the bottom, ability of the top, and so on. Pretty much the same factors by which any commerical video is judged.
I can give you one hint though -- generally, most people are willing to trade off technical quality for intensity of action (at least to a point). An amatuer vid probably won't be able to compete in a marketplace full of high quality product if the content is essentially the same. However, if your girlfriend is genuinely, outrageously ticklish (see note below) and is willing to (a) be naked (or at least topless), and (b) let you tickletorture her mercilessly and non-stop for at least 30 minutes -- then you'll have something you can really sell. And let's face it, there's no point in taking the chance of having a home fetish video come back to bite you on the ass unless you stand to make serious cash doing it.
Note: If she's a laugher, great. If she's a giggler, or worse, a screamer, forget it. The number one giveaway for fake tickle videos is absence of real laughing. People who are ticklish laugh when they're tickled. They don't scream nonstop, or giggle and sputter.