Wow! 2004 and still worth $1400. I think the Ninja 250r had the best resale value of any motorcycle as a percentage of original cost. The new Ninja 300 has bucket and shim valves so isn't scheduled for valve adjustments so often. I would do mine at 30,000 mi. which means "never" since I will not have the bike that long. My only high-mileage bike is the Zero S with nearly 5,000 miles after 7 months of ownership. I like how you can just jump on it and go in cool weather without warming it up or riding it long enough to charge the battery, heat up the oil to get rid of moisture, or get through a tank of old gas. Range and lack of storage are really the only valid reasons I have for owning other bikes, not that having a valid reason for owning bikes ever enters into my thinking except to justify it after the fact of ownership.
Tires on the Zero are probably a weak link. They are good for rolling and increasing range, but just so-so for gripping...at any pressure. I have to be careful with all that torque that I don't spin out, and trying to ride on wet pavement is dangerous and to be avoided if possible with the stock tires.