I'm not playing 4E at the moment, and still with 3.5, but I like the change. If the Driders were indeed mindless monstrosities, then their form could be seen as a curse, but since they are indeed smarter, more charismatic (which means more self-confident and self-assured!) and wiser than baseline Drow, then it's far from being a curse.
It makes sense to be a blessing, but not one that everyone chooses to take. I'd even consider it an NPC-only Path of sorts that Drow Priests and Wizards can follow, or, in 3.5 terms, make it a Prestige Class or Monster Class, sort of like the Dragon Disciple or the Ghoul -> Ghast monster class levels, allowing the Drow to gradually ritually transform himself (with Lolth's blessing) into a Drider.
Making it a choice, with lots of rituals and deliberation involved, or something that requires direct divine intervention, explains why not every Drow Priest or Wizard ends up becoming a Drider, just as not every Sorcerer becomes a Dragon Disciple or not every Ghoul becomes a Ghast.