With a proper engine management, u wont have to change the engine internals on the m50. I've seen b4 people running 600whp with stock m50 internals. WIth just MLS headgasket and ARP headstuds, and proper tuning such as megasquirt(standalone), u can get almost 350-400whp. Non vanos engine is a very robust engine. Its easier to tune with standalone due to the non vanos head. It has stronger internals and a higher cam duration compare to Vanos m50. Read about it more.
I do agree that japanese engine such as 1jz/2jz are monsters! Not to mention the cheapness to run it. Well, to each of its own. Why not give the bmw engine a chance? Do more research and u'll know why. Its more expensive to be honest...but with a turbocharged bimmer engine, u can never go wrong!
im currently swapping in an m50 non vanos to my car,hopefully will plunk in a turbo next year with 10 psi of boost. I've been laughed by friends who are using 1jz/2jz in their bimmers. well, my money...my call. xD
my 5 cents
Chris