Isn't it true that lenses are at their sharpest in the centre, so the fact that you may be avoiding the edges could be a good thing, especially with cheaper lenses.
Yep. Cropped sensors have many positives and shouldn't be regarded as inferior imo, just different. They have more reach (relative to the pixels on the sensor) and also a wider DOF for a start, which can be both good (for macro) and bad depending on what you want etc etc... I quite like soft edges, vignetting and shallower DOF though.