Just did my IM swap:
My car: 2009 328i N52 Engine
Source of IM: 2006 Z4 from LKQ through car-parts.com for $158 shipped.
Additional Purchases: 6 ring of intake manifold gaskets and a throttle body gasket about $30
Labor: 1 hour research and read-through the DIY here + 2 hours of actual replacement time. This is a direct plug-n-play for my car, no problems with oil return line piping whatsoever, gotta love German Engineering.
Result: Feels normal on the low end, couldn't tell much gain or loss at midrange, but high end rpms can definitely feel the difference, with the non-variable intake, power would plummet after 6k revs, with 3-stage, did feel power all the way till 7k.
For under 200 bucks and 3 hours of work, it's definitely worth it.