Imo, to do something like SNK or Digital Eclipse do, releasing the game/games emulated or partially rebuilt, and having the emulator / wrapper painted in a way the technical side is masked, to be as resistance-free as possible.

Also, some people would whine if they found a ROM can be extracted/rebuilt from the game files, sure, but if the final product looks and feels decent and seamless, and from my experience talking to people like those, them usually saying things like "why should I buy something I can download for free?", I'd say these people whining are not the developer's target audience anyways.

As for tools for wrapping or rebuilding C64 games, I'm not familiar with any, but I'd check if the emulators available have licenses that allow commercial use, if they require official firmware files - which would mean having to license those if they do require, and if the game can be launched from terminal/command prompt commands - which then I'd make a binary / executable file with the command for launching the emulator with the ROM and needed settings.