Well, the dispel needed to remove permanent effects is based on a permanency spell (at time of casting it). But for example, sees invisible doesn't care for CL besides duration so it's no stronger or weaker when cast at any level. So it's a good spell (as well arcane sight) made permanent. As often than not when you face invisible foes or someone stalks you invisible, you often do not get time or even figure out needing it before too late. More so these levels improved invisibility is possible. Or ethereal entities.