I don't think time spent learning something you want to do could be considered a complete waste. I don't see how you could learn anything from loom knitting that would really help when knitting with needles. The method of making the fabric is too different. What is it you want to accomplish? If you want to be able to knit just about anything, then learning to use needles would make sense IMO. If you only want to make a scarf or hat, I'm really not sure what else loom knitters make, then a loom could make sense. It all depends on what you want to do. Asking here is not likely to get you a really balanced response, as Jan said we all use needles. There aren't a lot of loom knitters here. I'm surprised there doesn't seem to be a place for asking questions about loom knitting specifically somewhere online.
I should never overestimate my basic arithmetic skills.