Just my opinion, but when I see these exact rifles in 98% condition, they generally sell for about $450. So, just based on that, for someone who is a shooter, one of these in mint condition may be worth $550 to $650.
Now, there are some people out there who love collecting Marlins. So, to a collector, maybe it would be worth more? But probably not, since it is not a vintage rifle. (Rifles made in the 70s just don't have much collector interest when it comes to levers.)
If you are looking to sell it, label it as a classic cowboy rifle, pre-safety, mint condition, solid walnut stock with no checkering, and ask $595. It will probably sell.
Your big problem is that I believe that Marlin is now selling classic cowboy type rifles in .30-30, and although they have a crossbolt safety, it is pretty easy to buy a kit to remove the safety and replace it with a plain screw head.
Hope this helps. I would love to hear some other opinions as well.
Regards,
Mannyrcok