Are you moving to the suburbs? If not then surely parking plays into the equation. Do you have a garage for the Maxima, or do you move it 3 times a week?
I live in midtown and pay $200 (w/ taxes) for an indoor lot through our building. Market would be twice that and I'm sure BH is in the high 300s, no? I've paid cash for last four cars so no payment, high deductible insurance and the sweetheart parking makes it easy to justify something I never use more than 3-5 times a month.
I'm guessing you have family & in-laws nearby who like to see there grandchild often. I walk to work and haul the kids around to school & events via public transportation. I rarely use the car as a grocery getter, it's just a weekend escape pod. I suppose you drive over to Red Hook Fairway or Gowanus Whole Foods?
If you're doing alternate side and staying in BH, I'd stick with the Nissan. At 140K you have years of good use ahead. It won't impress anyone but there are more important uses if your money. Regarding BMW, yes the 3 series is an impractical family car, step up to the 5 or go with the Infiniti if you're set on getting something newish.
Alternate Side Parking is only Monday and Tuesday by me... Parking is somewhat easy in comparison to other locations on my block. We usually drive on the weekends, a lot in the summer. When we get home on Sundays I'll find a spot on the Tuesday side and my wife will go move it to the Monday side around 9:30.
We took a ride to Philly last month and the car starting shaking over 65 - I had the wheels balanced and it didn't solve the problem so it has to be something a little more serious. Driving the car, it just doesn't feel safe. The airbag light is flashing, the ABS light is on, service engine light is on, traction control light is flashing, etc. etc. Basically, after beating the #### out of this thing for the last decade, it just doesn't feel safe and I don't want to invest a few K into fixing it... New problems will be around the corner after I fix the current ones.
After doing some HW last night, the 3 series def isn't practical and the 5 series might be a little too expensive to park on the street... Going to compare pricing from an Accord, the Infiniti, & an ES 350 - If the monthly difference is around $100 or less between the Accord and the Lexus or Infiniti we'll go with the nicer car.