I don't know what my parents paid for that set but it couldn't have been cheap. And my father's parsimony in those days was legendary.
I played with Legos until I was at least 15. I built worlds, made stories, had adventures. It was amazing. I would build a car and play with it for months, until I grew tired of it, and then I'd tear it apart and build . . . another one, different. (The red eights were jet engines, in case you didn't know).
So when they were "age appropriate" for my children (all boys) I naturally bought them Legos. But I was disappointed. The Legos came with instructions to build the thing on the box. Now maybe this teaches something about following instructions but I think it stifles the imagination. And my children didn't ever build their own things, as I did for almost a decade. They loved their Legos, they'd build the thing, put it on the shelf, and look at it. It seems part of childhood was missing. (UPDATE: One of my children just informed me that they did, indeed, build original creations out of Legos.)
I need to thank my parents for giving me that first set of Lego (I still have what's left of them somewhere). I cherished them and mourned when something was lost or broken (the gray rubber tires only lasted a few years, it seems). A few other sets supplemented my original supply but I still have a special place in my heart for that original three-color set (especially the jet engines).
I think that Lego set got me interested in science and engineering. I think it started me making up stories, something I do now full time as a writer. That was probably the best toy investment my parents ever made. It opened my imagination in ways perhaps even the creators of Legos never imagined.
What toy or gift helped put you on the road to your chosen field?