ive never touched a vex kit so i cant say much about that but as for mindstorms, the more time you put in the more you can get out of it. if you wanna just tinker with it and not worry about just using lego pieces, sensors are not hard to make, and 3 sensors? pffft. even with the ris2.0 ive been able to stick in as many touchsensors as i want. all you need are switches. available from your local broken electrical appliances. and wire and time and soldering skills help but w/e. motors, think of relays. and then if you make a transmission... and with 2 motors you can theoretically have infinite functions.... you just cant do them all at the same time.. btu thats why you have 3 motors. lol. but its theoretical because the more functions you add the more power the motor's gonna need to do the same output. so well. im blabbing on agian.
anyways. the rcx is a great startig block.. i love how you can expand using only lego parts too. multiple rcx communication is great. and yea. i love it.
oh and lego's target ages are miles off. or ages off... or they just dont work.
i know some people who cant build the a decent looking car at my age right now. so its all about how much you've been using legos, or knex, or any osrt of building "toy" ............ ok... lost waht i was gonna say. nvm.