Plus if you started running individual lines to everything you would have to figure out a way to balance the flow going to each one...In other words some would get a lot of water and some would hardly get any....It would be a pain in the neck to do...
Umm, nope. 'Closed systems' will always equalize pressure throughout the entire loop. If you add another pump, you do not double your flow rate at that particular point, but you might negate some of the loss put into your loop from your blocks and such.
*Look at exhaust systems for cars and race cars. True Dual exhaust systems come from the motor, straight back, to a 'CAT', from there, typically there is whats called an 'pressure equalizer'. This is no more than a pipe that connects the two lines together. Since the exhaust comes from seperate outputs on the engine, it is combined again later on before it exists the car, to equalize the back pressure in both of the exhaust lines.
Now, do to different compnents in each of the loops, you might have a small difference in the pressure between the two lines, but the flow rate should still be close to the same. You dont have to do any crazy science to balance the lines though....they do it themselves.