Yep, but typically people don't like to hear what I have to say...
I'm pretty spot-on with classic Datsun and Nissan valuation, but the best rule of thumb is this: It's worth exactly what someone just paid you for it. Not what they offer, not what you're asking. What they paid. Problem is, we don't know that until the deal is done.
So, if you want top-dollar, list it in an auction (whether it be Ebay or BaT). Start it at a reasonable number $5k. If you're confident in your car, and your photos, then it'll bring market value.
Quick and dirty: The auto trans hurts it, the 2+2 configuration hurts it. Mileage and originality helps the value a lot.
I'm gonna go out on a limb and say this: If it were in my collection and I were selling, I'd list it on BaT.
Here's a helpful tutorial - Your results are DIRECTLY related to how serious you are about listing it properly. You want all the money, you do everything listed in this article:
http://datsunforum.com/selling-on-bring ... -tutorial/
You can peruse past sales (although most all of these are 5MT, 2+0 cars) to get some ideas.
https://bringatrailer.com/nissan/300zx/
Good luck!