While I don't see the 335is as "plentiful" relative to other non-limited production passenger sport coupes, it is much more rare than any other E9x of any kind, M3's included. What I think is that it will always fetch a higher selling price than any other 335i, but it probably won't ever be worth more than it stickered for (inflation adjusted), unless someone never drove it and sold one at auction in 2035. You can collect anything you want, but I'm not sure how rare this car will be. I'd actually be interested in knowing how many they produce in total vs a car like the RS4 which is pretty limited.
I think the most current true collector car to be that BMW has made is the E46 M3 CSL. I'd also say the E36 M3 LTW is in the collectible category, as is the E36 M3 EVO.