If you use a library like fm's liquidcrystal replacement library,
then you won't need any additional Arduino pins to run 2 LCDS if you are not using
When using the SR3W interface there is one free output pin on the SR.
(assuming no backlight control is used).
You can then use that free output pin on the SR for the E signal on the 2nd LCD.
To do that you simply wire up all the pins for both LCDs the same except
for the E signals.
Then wire each E signal up to separate output pins on the SR.
In your sketch you will declare the two constructors with the pins for each LCD.
Each LCD will use use the constructor that specifies the 3 arduino pins
and the 7 bits (pins) from the SR but does NOT enable backlight control.
That will allow the library to know about and be able to talk to two different LCDs
but share the same SR to talk to both of them.
No extra components, no extra Arduino pins.
The only draw back is you lose the ability for s/w backlight control.