Mixing different brand cables a good idea or not?

Personally, I don't think it should matter much. The advantage of staying within a single brand might be that they are all designed to have similar sound characteristics which might give you an indication of if you'll like another product from their line.

I'm starting to think that some of the companies may have it right for one type of cable and not the other. From everything I've read the design criteria for interconnects and speaker wires are very different so when I see companies using very similar designs for each it seems, at least to me, that they may be great at one type of cable and the other is just to fill a market niche.

Its horses for courses for me; but a full set from Cardas or Transparent etc. will be great without having to worry about matching.

I am in the process right now of trying different interconnects and speaker wire. I bought matching cables from kimber kable , nordost and paul speltz. i have been mixing different cables with each other . i found i like kimber for interconnects best . with paul speltz anticables for speaker cables. The kimbers add bass to the bass shy maggies i have. and the speltz cables i like much better than kimbers 8tc speaker wires . so imho it does not matter.