I don't think that having distinct, separate hitsparks for high/low attacks is a very good idea, though it's extremely close to something that BlazBlue and Skullgirls do.
So, for example, in Skullgirls, if you're blocking high, and you get hit by a low attack, an orange "!!" symbol appears over your character's head to show that you were blocking the wrong direction. Similarly, blocking low and being hit by a high attack shows a blue "?!" symbol over your character's head.
This presents a couple of advantages over having entirely different hitsparks for high and low attacks. In short, it's expected that you'll experiment with moves to see which ones hit high and which ones hit low. We assume that you already have this information. What the block symbols do is reinforce that information whenever you make a mistake, but only when you make a mistake, and make it clear that a mistake was made. It's not important for me to be reminded that Oleander's 6C is an overhead every single time I get hit by it. She might use that for a combo at some point, where the fact that it's an overhead is completely irrelevant. It's more important that the game tell me that I was hit by her 6C because I was blocking the wrong direction, only when I'm blocking the wrong direction.
Having this can help reduce the number of "What the hell? I totally blocked that!" moments. I think it's worth implementing.