I disagree
Catalyst IS the centre of operation in a number of (not all) show setups. Not only is it the replay system, but the matrix switching, projector control etc.
You may not need to 'operate' catalyst during showtime - but you will need to set it up - in some cases, I've had config changes at each venue. therefore you need monitors! A decent DVI DA is £100-160
2 x macbooks may be cheaper - but performance is nothing compared to a well spec'd MacPro. From my personal experience of touring Laptops - i wouldn't suggest it - security, vunerability, increased setup time. Fine if you're a small operator - but go look at any big video rental company around the world - theres a reason they've all purchased mac-pros not laptops....
Ive actually used the same size flightcase for a number of different 17in monitors over the last few years - all i've had to do is change the foam inside slightly - which is fairly easy and costs nothing.
Once again - this discussion comes down to the requirement for your show. If you touring with no equipment (ie venue provided) then a laptop makes sense.
If you are touring with a full lighting rig, sound, and video screens or projection, then a well designed case and a mac-pro would seem more sensible.
Its not necessarily all about the mac - You still have to consider scan converters, artnet equipment, UPS, and peripheral equipment that you may use with catalyst and for the requirements of your show.
my catalyst rack and iPC actually fits in the back of my car...