It doesn't add anything to the value, the hardware store guns usually had birch stocks instead of walnut, though in the case of the Marlins, they all used birch, some just had different patterns on the impressed "checkering". Only the 99C Marlins had walnut stocks, IIRC.
I have a Coast-to-Coast M40 myself, basically the standard model with 22" barrel and full-length tube magazine. Grandma had bought one for Grandpa and I liked it. My birthday was coming up, and Dad bought one for me, too. I killed a truckload of squirrels and rabbits with it, and still have it. The price in 1971 was $39.95. I got a Weaver D-4 scope for it on Christmas, and with that, I made the local squirrels terrified of me. Even running rabbits weren't safe, I killed a lot of them in front of my cousin and his 20 double.
I'd reckon that yours might be worth $150 now, but you can buy a new one for nearly the same price now. The box magazine guns seem to be a bit more reliable than the tube guns. I know mine was not stellar in reliability, particularly with the promotional ammo I could afford back then (Winchester Wildcats, Remington Mohawks, Federal Champions, they had loose bullets in the cases, and only shot "okay") That led me to CCIs, which were somewhat better quality.