Tools should be as simple as they can possibly be. But no simpler. Tools that adhere to this MinimalistDesign far outlast their competitors.
TracVsFitnesse is a fine example of this philosophy. Trac is a lean, toned, sculptured tool, the very embodiment of an OpenSource TechnologicalChangeVector. FitNesse is a fat old cow, bloated with unnecessary features, mired in proprietary development, and encrusted with poorly formulated hyperbole. It was almost obsolete before it started.
See also KeepItSimple KeepItSimpleMinimalization KeepItSimpleStupid MakeTheSimplestThingThatCouldPossiblyWork AsSimpleAsPossibleButNoSimpler