Keep the cables the same throughout the system?

I think you should stick to the same manufacturer for speaker cables and interconnects. I am not so sure if it matters for power cables to be the same as SC and IC, anyone any views?

Only if you have all the same Manufacture equipment designed to work together.

If not then mix and match is the way to go.

Each peice of equipment will have its own needs when it comes to power cords, interconnects, spkr cables etc.
Some cables will improve the sound, others may may it worse.
Dont limit yourself to taking the easy road.

No - I'm not talking about moving to another brand - but possibly going to the step beyond the spellcaster on the CD/Pre link (to the sorcerer or even illusion)... while keeping the spellcasters between the pre/amp.

To my knowledge the Spellcasters have been replaced by the Trinium XL.

Would I be limited by the lesser of the cables?

I use Audio Magic cables exclusively in my audio systems and have 'moved-up' within the line with excellent results. Mixing cables from different manufacturers just doesn't make sense to me!