The key word here is porsche.
Since the 500E was a collboration by mercedes and porsche, you really can't go wrong. its like having the best of both worlds.
Sedan meets sports car...
Personally I would go for a 500E. you can find some very very nice examples for around $30k
I have seen some as low as $22k with a bit more on the odo, but its hard to find one at that price with decent mileage.
I myself would rather spend $5k extra for a nice low mileage one.
I have not driven a 500e, but I myself would buy a 500e because it is a work of art, a sportscar hidden beneath the shell of a sedan.
the 400e's do drive nicely, but the suspension in the 500e, the flared fenders, and the massive rubber, make for an awesome combo, not to mention the awesome power. I'd buy a 500e in a second if I could afford one.
Don't get me wrong, both cars are great, but the 500E I think has a more collectors aspect as it was only produced for a few years and it really is a unique car that you will most likely not see again from mb, now that every model comes in an amg version just about.
Alon