My GF doesn't follow cars at all but she thought an '08 M3 sedan looked older than my '04 E46 coupe because of the tail lights. (It's a little different with the '09 M3--its lights look pretty modern. I ordered an '09 as opposed to picking up a bargain '08 for this reason alone.)
IMO the E46 LED's look quite modern and blink much more brightly and engage more crisply than any E9x lights right now since they are true LED's--both braking and just driving around. And they have adaptive brake lights, an extra ring that engages when ABS is engaged...
I think E46's have different "dated" features such as the strip moulding down the body lengthwise and general boxiness... but the tail lights definitely look great for the '03.5+ LED's.
M3 Sedan LCI - AW/Black - 6MT - no moonroof - no folding seats - RAC RG63 - clear bra by Omega Werks