Parents, do not splurge when your child is "in" thing but you know that grow out of it?

What I mean is when your child has a new favorite (Dora, SpongeBob, Cars, Princess, etc) do not buy many things that revolve around that, but you know you will grow out over time? Or do you keep everything in moderation and allow it to become a collection of things. I ask because my in-laws bought my daughter in excess of what it is at the moment and I'm trying to convince them to keep it in moderation. My daughter just went through the Hannah Montana stage and everything that hannah montana (clothing, bedding, posters, dolls, jewelry, pens, perfumes, shoes, hair ties, lamps, alarm clock, guitar). I understand getting your things you like but my husband and I try not to take anything by overboard as we know it is a stage that will soon .. It made me realize (and who went through the same with Dora) to be mad when they learn that is something. Opinions? And what to do with them when they are no longer in it?

Maybe you could gently explain to her in-laws that current trends do not last long and gifts will be thrown to one side of the art "and that instead if they wish to purchase a gift you might choose something that will be helpful and appreciated any longer. I am sure they would be happier buying something that will be assessed in the long term. E-bay things no longer used and maybe used the money to create a bank account for your child so they can learn to manage (and see) your own money!