Whether you get unlimited mileage or not on a free rental depends on whether or not you would have gotten unlimited miles were it a paid rental. It's booked like a paid rental, but the difference is they eat it.

The answer is whether you are using a CDP that gives unlimited miles on one-ways with a higher base rate, like AAA, or if you are using a contract flat rate code that gives $35/day plus 47 cents a mile or whatever.

You're correct that outbound one-ways from the NY metropolitan area, or any other expensive, high-demand strong urban market, can be a good value using points, since they will almost always be expensive. One-ways elsewhere may or may not be a good point value, depending on the paid rate. Although, sometimes RQ DRIVE can give a decent rate where you might want to save your points for something else.

By the way, where are you going?