I think you better stick with whatever you have at the moment.
They way I see it, you don't need a tablet that senses even the air around your pen to be able to make amazing artworks. I could make such stuffs with just a Nintendo DS... which has a screen that is far smaller than the smallest tablet out there, with an Oekaki style homebrew application with no layer and filtering support, then... why can't you? And with a tablet almost twice the size of the surface of the DS? That is not to say that I am better than any of you, that is just to say that the art tool doesn't really matter. And small stuffs like the DS sometimes make a big difference. Don't underestimate the tablet you have, and use it wisely.
P.S.: And here's another con of drawing on the DS: Sometimes, you get jumping lines. Or in other words, you put your pen down, and a line appears randomly on your artwork.
Those are just my personal opinions. I myself loved how the DS performed so much, I purchased a Graphire3 off eBay. It's coming somewhere next week... hopefully. Maybe then, I'd have more to base my opinions on. But for now, I'll let my artworks speak for me.