I go agree that it doesn't make a whole lot of sense for what is essentially a droid to open up and have a cockpit. It's just for play value of course, kind of like how you can get "inside" one in Battlefront 2.
One thing though that does interest me in the cockpit is I think that might bring about some customizing potential... kind of like that "pod" or whatever the hell it is on Mos Eisley.
...God, Stephen Hayford's older work is still amazing.
BTW, I saw another of the Spider Droid today at Target with the other vehicles, but two employees were in the process of frantically taking them and a whole bunch of Legacy figures off the shelf... but, they left the Galactic Hero stuff out, as well as the Commander Fox kid costume...