It will be waaay hard to ever sell a 335i without Navigation.
I'm not saying you'll get your full $3K option cost back in the sale price, rather dozens (hundreds?) of buyers will simply pass over your car in favor of one that does.
I regularly browse the FS boards, here and other places. So many "stripper" cars have comments like "excellent and beautiful car, too bad no Nav or I would be all over it".
It's the equivalent of A/C, IMO. Even if you live in San Diego and don't need A/C for 360 days of the year.