As you mention, the only component for the crossover is a single capacitor for the tweeter to stop low frequencies getting there - the bass driver is effectively connected direct to your amp, so it's giving you lots of the benefit normally associated with active monitors, hence the appeal of the midrange in the sound.
I believe replacing the capacitor is a common enough thing to do, but i'm not sure it would avoid the basically not great quality of the tweeter, which is the weakest aspect of the implementation. Now if someone knows of a replacement tweeter which could be fitted, that would be really interesting!
BTW, love my pair, had them since 1993.