When you mouse over a target, a red outline is shown around it. The outline is even displayed over spell effects. Simply adding a toggle to always show the outline for your selected target would help to fix the “I’m blinded by spell effects” issue.
It could also be made to display over other players, which could look a little strange, but would allow you to see small targets infront of big characters. For example, when a asuran boss does a telegraphed ranged attack, but it’s hidden due to other characters standing infront of it.