Dual exhaust belongs in cars that come equipped with it already such as the M5, OR E90 M3. Just by looking at them you can tell deserve dual exhaust! I have seen some e36s with dual exhaust though, just not my cup of tea. It makes me giggle lol. It reminds me of guys that I have seen in their tricked civics with large dual exhaust systems in a little 1.8 four banger sounding terrible to me, but I guess it sounds powerful to them.
All in all its up to you and what you do to your car since you are the owner.