I got this a lot when I was preparing for my first trip. My daughter had just turned 2 the month before, and everyone said that it was a waste, and that she wouldn't remember it, so why were we wasting our money? I told the critics that she won't remember me staying up rocking her at night, singing her lullabies, taking her to the park, going to the zoo - heck, even just LOVING her - but I still do all those things, because that is what you do with your kids. You let them experience new things, even if they won't remember them!
My 2nd daughter was 6/7 months old when we took her last time - and no, she doesn't remember going (obviously!) but she had a great time, and I'm looking forward to taking her in March at 2.5 years.
And of course its expensive - any good vacation is