I've had a bit of a think about it. This looks like an okay system. You could add a team's Competition Points to it's Goal Difference and then divide that total by the number of games they've played. Again, you must make sure you have a fair few games to go on. Using this year's EPL table so far:

Team Pld GD Pts (RATING)
Chelsea 17 25 40 (3.82)
Everton 17 7 36 (2.53)
Arsenal 17 22 35 (3.35)
Man Utd 17 12 31 (2.53)
Middlesbrough 17 7 29 (2.12)
Liverpool 17 7 27 (2.00)
Aston Villa 17 3 25 (1.65)
Charlton 17 -8 24 (0.95)
Bolton 17 1 23 (1.41)
Tottenham 17 -1 22 (1.24)
Portsmouth 17 -2 22 (1.18)
Newcastle 17 -4 21 (1.00)
Man City 17 3 20 (1.35)
Fulham 17 -9 18 (0.65)
Birmingham 17 -5 17 (0.71)
Norwich 17 -11 15 (0.24)
Crystal Palace 17 -7 14 (0.41)
Blackburn 17 -14 14 (0.00)
Southampton 17 -9 13 (0.24)
West Bromwich 17 -17 10 (-0.41)

Now, I'm not totally sure how much advantage to give for home grounds. Perhaps 1 goal??? So say Arsenal is playing Man City at Arsenal, on these ratings they should win by exactly 3 goals. But most of them won't work out that well. Not quite sure what you should do when you have a team winning by .67 of a goal or something.