My decision making with regard to chosen tactics basically revolves around two notions;

1. How do I want to fish today

or

2. What is the most effective way to catch fish today.

I find myself switching it up either when I am bored by either repetitive motion, or not catching fish...respectively. Maybe it is just the ADD, but if I do any one thing for long enough, regardless of how cool it was when I started, i get bored eventually. For me a big part of the reward comes from overcoming a challenge or building some degree of skill or knowledge. With spey casting at least, I do it so infrequently that each time is a lot like starting over, and I get a fair amount of reward out of just remembering how to get the line and hook out there.