The SPI terminal is for Gamma and Internal Configuration
It seems that you might be able to use the drawing functions internally to the screen using SPI, and that looks like a big pile of fun to figure out, though everything one would need is in the datasheet(s)
Its a digital RGB screen, and thats a bear for an arduino to tackle, your going to need a 6 to 20 Mhz dot clock (how fast the pixels are flying by) though I am not fully sure why the 8 bit mode needs a typical 19.5Mhz and the 24 bit mode needs only 6.5Mhz typically.
And then you got to send it sync signals, I mean crap man there is 30 signal connections to make NOT counting power, ground, negative power, and the touch screen part which is the little header you see flapping around to the side. The claim that
You may now control a 320*240 touch screen with a 8051, and of course Arduino without any extra circuit!
Really depends on your intention. If you want a full featured video display, then no, you really cant, if you want a LCD to draw simple line art and text on then yea maybe ... but I doubt anyone has tackled it yet.
I am sort of interested in it though