If we look back to last season for an example of how many points a great keeper would save:
2-1 win v Everton at home, De Gea saved a penalty and pulled off another great save. Could have been a draw or defeat for United, so that's 2-3 points saved
2-1 win v Arsenal away, De Gea saved so many shots from Arsenal in that game. Could have easily been 2-0 down in the first half making it almost impossible to claw a result back. 3 points saved.
3-0 win v Liverpool at home, at most if could have ended a draw for Liverpool, we put it out of sight quickly but brilliant saves when we were 2-0 up could have ended the game in a draw, 2 points saved
2-1 win v Palace away, struggled all game and De Gea pulled off a brilliant save to seal us 4th place, could have ended as a draw so that's 2 points saved.
9-10 points saved from those games. There's probably more I'm forgetting like the wins against Stoke and West Ham at home where we were pegged back near the end of games, but those particular games above stood out for me. When you take every game in account it's probably about 15 points saved, just an estimation.
It's obviously all very highly subjective, there's no guarantee that United would have dropped those points if there was no De Gea as they could win those points regardless, but it does show that a good keeper can do wonders for a struggling defence.
Yeah, but the against Palace was a save you expect most good keepers to make. Also the first game against Arsenal, where I am sure Valdes would have made the saves (I was more impressed in the FA cup). Against Liverpool I do agree, but not with the number of saves, as I am sure Valdes would have made the one on one saves (he proved it against Hull), as Sterling was really horrible in these situation, he literally just shot strait at de Gea but I liked the save against Balotelli. Actually, the one on one I am sure Cillessen would have made them and people complain against him.
Just look at the second goal against Swansea and the blame Romero is getting (and he should). If these de Gea saves were WC, or brilliant, then we can't blame Romero for the goal against Swansea, because in these sitaution the only thing a GK has to do is to position himself corectly and if the striker scores, great job from the striker if not it's mostly the strikers fault.
Don't get me wrong, these saves were esential and good, but you shuould expect them from a good keeper and I don't think they should count towards this discussion. It's like with Romero against Tottenham, we could say that he saved us 2 pounts, but I actually expect a GK to save these (it were still very good saves).
I do agree about the Everton game, the last save was brilliant, but also the one few minutes before. One I think you are forgeting is the one against Newcastle, that was also a really good save in the last seconds.
He also conceded a dodgy goal against Villa, but we won the game.
De Gea will save us points for sure, but he could also cost us some as he is not controling the penalty box, but people just ignore it. I think the real question in this topic is the number of points a GK gives from saves most of the GK wouldn't make and usually it's not more than 5-6, but that is also a huge number.