"would it be worth more...."
Worth more to you or worth more to someone else? If you don't plan to get rid of this car, build it how you want. You'll be happier with it. If you're planning to sell it and make some money, keep it stock. Of course, plating all the brackets and bolts, replacing the seals, doing the metal and body work to an OEM level, etc.., is going to eat up a lot of money. If all you change is the colour of the valve cover and engine block, that probably wouldn't keep a purist away. A weekend or so and all that can be changed back to original. If you change the interior colour, resale would be better if you kept it another factory colour that was available on your model. i.e., changing it from beige to black would be better than changing it to green. Don't worry too much about the engine, as far as I know, the engines and transmissions are not number matched in Z cars. In general, the block and head (L28, N47, etc) are matched with certain years and models but the number following L28 on the block is not matched with the VIN.
"just wanting to hear general consensus"
It sounds like you admit that you've heard it, "280, do whatever you want with it". Truth probably is that the general consensus in 2010, 2020, and 2030 are likely to all be different. As 240's and 260's keep getting snatched up and their value goes beyond the budget of a mere hobbyist, people are going to shift focus to what's attainable. The 280. The 280 will never be as collectible as a 240 but in 2030, it will be more collectible than it is now. That's my prediction, based on nothing other than my gut so, not worth that much huh?
I have wrestled with your questions a lot. My situation, I'm currently restoring a '77, beige metallic, beige interior, 5speed, lower and upper body mouldings, etc. That beige on beige makes me cringe with how ugly I think it is. I have what I think is mostly an acceptable list of mods without deviating from factory too much. Anyway, pm me if you want to bounce the acceptability of different mods off each other. Or, since this is your thread, you can open them up to everyone here.
Oops, I can be more direct but again, this is my opinion and I'm by no means a long time Z guru so, add salt.
Does changing the color of the engine block change the devalue the car? - Doubtful, unless you're going for a concourse resto
Does changing the interior color from the original change the value of the car? - Maybe. If you keep it another period correct colour, probably not. If you deviate from an original Datsun colour, it could definitely bring the resale down. You'd be looking for a buyer that wants whatever colour you picked rather than a buyer who is expecting to see a Datsun colour interior already.
Does changing the paint for another oe paint change the value of the car? Similar question will custom paint devalue the car. - Same answer as the interior. I'll add, if you change the colour, you better remove the windows, doors, trim, and paint the engine bay. If things are just masked off and the respray is obvious, that's a negative. Keep it the original colour or go all out with the new paint.
