The light weight, fat fender plus LSD makes the 1M still most valuable player....
1M light weight with the n54 easily tuneable add 160rwhp and 200rwtq over stock for about $2k with DP, fmic, dci, Cobb e30 map!
Easily add the above parts and an LSD to a normal everyday 135i and have a blast for 1/2 price say $30k.
Any BMW with the n55 is a downgrade because it simply won't put down numbers like that for the $$. Probably going to run $50-60k for a 235i with software, fat fender body kit, and an LSD and new car depreciation.
New M3 is well worth the $$. 4dr utility, Lightweight parts that just can be fitted aftermarket, LSD, and stock power levels are just about where a modded n54 would be. This has got to mean 500hp is close and will be inexpensive.
The only downside I look at is the depreciation of a $70k car being brand new. 3yrs old this f80 will be the best bang for the buck at a 20-30k discount with the kinks worked out!