People will generally be more interested in something they haven't seen before, like unique gameplay or unusual graphic styles.
Think of Minecraft, that started out in the way you describe with the alpha version being cheaper. It took off and picked up an expanding fan base because there was nothing else really like it out there, and it did what it set out to do very well.
If you just make a Mario clone or something that might be considered more 'mainstream' but it's been done a lot, so people would generally be less interested in it.
Also with alpha funding it's more suited to a game that can gradually develop and be replayed over and over, such as sandbox type games (Minecraft) or games that are solidly based around it's engine development like Voxatron (or at least that's how I see it). If you have a platformer game for example, the alpha will be a buggy version of the game, by the time the bugs are ironed out and it's released people who've played through the alpha have basically already played through it all; what I'm saying is this method of funding is better for open-ended games rather than something linear (in my opinion)
tl;dr - NEW IDEAS ARE GOOD!