This is absolutely not the answer.
When I was reffing, my area would make the refs give 3-2-1 for all grades, and it was a nightmare. I would always delegate the task to someone else. Either my Dad (who always liked to come along to the footy), or my Touch Judges, or the Ref's Coach sitting in the stands.
There is just far too much going on for you to properly take in who is playing well.
I once saw a guy pick up the 3 points in a reserve grade match. He only played 15mins, his team was down by 3 tries already, and he got taken off the field in the back of an ambulance. The ref gave him 3 points because "he's always good". Just farcical stuff.