I don't see why they wouldn't extend the dates, it's proving to be popular, with nights "selling out". Seems like a no brainer to continue to offer them (especially when crowds are only going to continue to grow and crowd the park). If I weren't able to live as close as I do, I'd certainly plan my trip around the After Hours and would prefer that to regular day tickets ... lol. But I have an annual pass so it's hard to justify buying a ticket to after hours. But I really really enjoyed the one I did at the Magic Kingdom. No crowds and walking on to almost everything really was worth the price. I think four hours would be nice, but I was able to accomplish a lot in two and a half hours (the event is usually three hours, I believe).
Although they do sometimes now offer Extra Magic Hours for Passholders (I won't call it an "event" because it's not, it's EMH for passholders that you have to sign up for and it's not for lowly silver and below) ...