Help Me: Building Themed Decks

One of the aspects of Magic that I feel is definitely underexplored is the notion of the players being planeswalkers dueling for supremacy over some corner of the multiverse. However, the more competetive players get, the more the flavour of the game falls through the cracks, as the game aspect is emphasized.

One of the best ways I've found to capture that flavour is to play a themed deck. When I'm playing a deck full of zombies and reanimation spells, I sort of feel like a grim necromancer when I play it. When I play with a bunch of stuff that gives -1/-1 counters, I feel like a plague lord. However, these decks tend to be noticably inferior even to other casual decks. In addition, there is no clear line between a deck with a theme and one without a theme.

What I am looking for is a set of general guidelines or even fixed rules that might be used in arranging a tournament focusing on themed decks. Obviously, to allow for the greatest number of possible themes, easy ideas like "only one creature type" or "only one colour" are too narrow. However, I don't want to leave the themeliness of a deck solely in the hands of the deck builder, since then it becomes more a matter of justifying the themeliness of any deck.

Is it possible to come up with such a set of rules? I'm not sure and I'm looking for input there too. Is this a feasible project? If so, I'd appreciate any help I could get in setting up these guidelines.

Thanks in advance,
Ephraim