I have some timings here:
SPI is faster, but needs an extra wire or two.
Note that the Wii nunchuk uses I2C, so presumably it is fast enough for gaming.
There are cable run limits for I2C (and also SPI). However there was a post recently from someone that was able to get SPI to work over quite a long distance (60 meters?) using RS485 transmitter/receiver chips. Also there are I2C extender chips.
If you are writing to the screen (ie. updating the LCD) then the extra speed you get from SPI might give you faster updating. If you are just reading touches I doubt it will make a heap of difference.