Battery degradation is a fact of life with an EV. In 4 years and 36K miles it's had some, it's just a matter of finding out how much. My 2013 is down one bar and shows 83% SOH in Leaf Spy after 34K miles, but it came from San Jose and heat was probably a major factor.
The thinking has been that battery prices will drop precipitously in the next few years and replacing the traction battery won't be as big of a concern. There is also the fear that no one will bother to produce a compatible battery in the future since technology will leap forward at such a pace that it won't make economic sense to bother building one. I'm personally hoping that doesn't happen any time soon.
You also realize that Nissan warranties the battery to not lose over 30% of it's capacity in 5 years/ 60K miles? There is little chance of that happening by the time you hit 5 years from the in service date, but is something to consider.
Since you mentioned you were a teacher and with a user name of sciencegirl, I'm going out on a limb and guessing you might be a science teacher?
Newton's Laws of motion becomes very important with an EV. I don't run in ECO mode, but I do find myself looking for any excuse to coast down a hill or use regenerative braking when I need to slow or stop. I try not to use the HVAC more than I need to and I keep my tires inflated to 42 psi. All things I read about here that I thought I would probably ignore since I have a 16 mile round trip commute, but squeezing out every available mile seems to come natural when you have the range of an ICE car with a 3 gallon tank!
The bike could be a good backup in the spring and summer, but I doubt you'll opt for that during anything approaching winter conditions.
The GOM readings are just that right now, and hopefully way off.
From what I can gather, the 2015 "lizard" battery is holding up the best, but you have to figure out what you can afford and what you are willing to spend for that. Obviously, I opted to spend less and take a chance on a 2013 myself. I do love driving it, and I have a lot of options on what I can drive!