Actually, a slight revision to the above. I just walked up to the showroom again for another look. The back is not as bad as I remembered, but the front is worse.
Right next to each other is a Gunmetal grey E90 320 saloon UK£26,500 and a bright red E46 convertible UK£28,000. So not much difference in the money Inside the convertible has some "M" parts, some carbon fibre and half suade seats. The E90 has parking sensors, nothing else of any great significance. For me the E46 wins it easily.
As a side note, the E90 dashboard and interor looks much more bland than the E46, although the 6 speed was nice. Looking at the front of the two side by side I have difficulty putting my finger on what I don't like about the E90. However, it seems that the distance from the bottom of the headlights to the bottom of the front fender has too much unbroken space. It is hard to describe but it is as if the front fender is too big for the rest of the front of the car. From the back the E90 rear lights are ok, but they look awkward as if added as an afterthought, as if they were meant for a different car. Where as the E46 lights fit the rest of the rear of the car's symetry perfectly.
Just my opinion