My girls LOVE legos. They have a few of the new 'pink' ones but mostly play with our 20 year old lego collection. They don't think of the girly legos as 'real legos', for whatever reason.
It _is_ disheartening to go into a lego store and see almost solely boy-oriented sets, though. I note kids in Lego stores are roughly 60/40 boys / girls, but the sets are boyish.
Even with the sets there is still learning involved in lego or at least skill/work involved for some(the same people with the imagination before I would imagine). I'm young enough that I grew up with lego sets(actually I grew up with construx and built many a string controlled robot with them!) my favourites were the pirates ones and I still have them in a big box at my parents house. The lego sets I had came with a set of instructions on how to build whatever they were for. But the booklets also came with 4 or 5 pictures of other projects built with the same or a subset of the same parts but no details on how to make them. I admit I wasn't imagining a new thing and building it but I would always work out how to build what they showed and I learned a lot from that too.
The big problem is the movie-themed sets where all the children do is reconstruct scenes from a movie, instead of using their imagination to create novel scenes.
I still wouldn't call that a waste though anymore than I'd call model building a waste. They may not be using their imagination but that does not mean they aren't learning or developing other skills.
They are learning to follow instructions. Sure that's a useful skill, but 98% of school is teaching them that. What the more open ended lego kits teach is that you are free to create things constrained only by your imagination and the bricks you have. That surely is far more valuable than reconstructing a movie scene and having it gather dust on a shelf.
I see the sets as a way of defining constraint, i.e. establishing what an approved construction standard is. It then becomes possible for someone with extra bricks to invent a new model that fits in with the same scale/standards. Look at the fan-created models that scale to the modular building standard established by the Cafe Corner/Greengrocer sets for example. Sometimes a set of reasonable constraints leads to more creativity than there would be in a completely open environment.
It _is_ disheartening to go into a lego store and see almost solely boy-oriented sets, though. I note kids in Lego stores are roughly 60/40 boys / girls, but the sets are boyish.