I think I am correct in believing that the i2c connection will only use 2 pins whereas the serial connection requires several? I need all my available pins.
Um..... I use the Parallax 4x20 Serial LCD display... it only uses ONE line for serial transmission. take this simple code to send hello to the display

DIFINE OSC 20 'Always define the Oscillator your using !!

SEROUT PORTA.5,2,["Hello"] '9600 baud True Driven will send this to the display

And here are some other Good commands:

SEROUT PORTA.5,2,[$11] 'This command will enable the Backlight $12 disables
SEROUT PORTA.5,2,[$0C] 'This will clear the Display
pause 5

It is Very Easy to use and program.... remember only Power ground and 1 wire for serial communication !!!

view the LCD DataSheet here