You can always justify putting cool toys on your AR, as many (not all) have practical purposes. The light, for example, is extremely useful, and the cost can easily be justified. Night Vision, however, is extremely useful, but difficult to justify since GenIII models can run the cost of three pre-ban rifles or five post-ban rifles. I'm not a fan of the vertcal foregrip for semiauto, but the FA guys seem to like them. The entire series of rail systems (RIS, RAS, SIR, SMIRSH, SPLAT) can be justified if you have the cash. My rule of thumb is to keep everything within budget and prioritize. My two girls and their educations come first, so I'm relatively poorly equipped compared to some other AR owners I've seen. Best rule: If you can't afford it, you can't afford it.