I wouldn't have minded them keeping the franchise going if there hand't been like an 18-year-gap between Last Crusade and Crystal Skull. As it is, Ford looks...really really old...and cranky.
Arvie, the holy grail in Da Vinci Code has absolutely nothing in common with the Holy Grail in the Last Crusade. They don't even call it holy grail in that shitty book, they call it SANGREAL so as to make its true meaning more apparent. You said "His idea was to be about the holy grail..again?" The Da Vinci code isn't about some magic goblet, it's about Jesus's possible descendants. Don't be obtuse.