Of course they will remember. It's an all-time record. Or do you think people are not remembering the likes of Raymond Poulidor or Joop Zoetemelk? It's not all about GT wins you know. How then would you consider Pantani a legend? Or Ullrich?
Valverde's legacy won't be GT wins obviously, but it will be his consistency, his longevity, his capability to win on every terrain, etc. You would need to go deep in the past to find rider with similar skills, and back then it was way easier to do things he's doing in the present.
He was never as dominant rider as for example Contador was in GT's, or Froome, or maybe Cancellara in the classics, but who else has a 16 years span between his first and last GT stage win, or between GT podiums? Who else has a 19 top 10 placings in Grand Tours? Who else has 7 WCRR medals? Who else has a 130 professional victories in the modern peloton while not being a sprinter? Who else was a top 10 rider in the world every single season for 16 years!?
And there are many, many more things in which Alejandro Valverde is unique in today's peloton, and that's the real reason why he is a legend.