As a fellow mediocre player, my sense is that the best way to prevent blunders is to slow down and enumerate the possibilities. Sure, tools will help, just like having the computer suggest the three best lines will help, but it kind of defeats the purpose of trying to be good at the game. If you're frustrated by missing something that you feel you should have seen, slow down and see it next time.
I've thought about having the squares show light shades of primary colors so you could see which side is attacking a square, and the composite colors would highlight contested ones, darker shades would mean more attackers. Like red/blue/purple or yellow/red/orange.