I agree that Valdes is for sure not a goalkeeping legend in football as a sport. I do personally consider him a Barca legend but I think more in the same way that you guys do, that he was a part of the legend of "Golden Age Barca". Almost every true starter from the golden era can be considered part of our legend based on their contribution to Barca's success. This includes guys like Pique, Alves, Eto'o, Busi, Abidal, etc. (and I'd argue that every one of those guys are bigger legends for Barca than Valdes). I'd say Pedro's legacy wasn't far off from Valdes' but his lack of longevity, form, and time as a starter in comparison don't classify him as a legend. The point is that everyone who had a notable impact on either of the trebles and all of the success in between has solidified their memory into Barca's history. The team's feat is legendary and they are part of that.
However, it's easy to understand if someone has a different personal definition of what a legend is. If they're talking about a 'legend' as a player who is practically at the level of worship in a club's history, it doesn't apply to nearly as many players. Under this kind of metric, the legends of the past decade are Messi, Xavi, Iniesta, Ronaldinho, and Puyol. Before them, guys like Cruyff and Pep. These guys are really ingrained into the folklore of the club. They're the kinds of examples that pointed to in La Masia and they will always be talked about when thinking of the club.