A 335 is going to be a higher cost maintenance than the N52, but most will say the 300+ hp plus the easy ability to increase it is worth it. With the 328 N52 you can get the 330 manifold for 25hp, plus a chip tune adds 20 hp, and everything after that becomes very expensive per hp gained. It is more reliable and trouble free versus the 335. If buying a 335, I would recommend getting the newest and lowest miles one that you can afford.
You might also consider the next gen F30 4 cylinder, which is very efficient in both power and hp, but then the noise of the engine, the electric steering, and the bigger car might not be your cup of tea. They sold a lot of them, so they will be coming down in price very quickly.
I went from an '01 325Cic AT to an '09 335 Coupe w/MT and it's quite a jump in performance. It's a different ride as the E46 but so much more fun to drive. It's only been six months and the little things have been under $100 a month so I'll see what it costs to own. My E46 averaged $110 a month for maintenance, a new set of tires and Style 197's plus all repairs.
I see this OP was 2016 -- but this is to help those that are considering moving up from an E46 to an E90.
In our family we have 1999 323i, 2000 323ci, 2001 325i, 2003 M-sport 325i (crashed and is now a parts car) -- We just bought our first 2006 E90 325xi with iDive.
We do all of our own maintenance on the "BMW fleet" and I can say that one draw back that I have found is that most of the BMW forums do not discuss issues and resolutions for the E90s. So if you rely on forums to assist you with diagnosing and repairing you will likely find less support for the E90s than you have experienced with the E46s.
Have a look at all the postings here and you will see that most go unanswered.
If you have an Independent garage or a Dealer that performs all of you diagnostics and repairs then this will not factor into your decision to get an E90.
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