318 replacement cams....

I would AT LEAST put just a "bit" more cam in, something along the lines of a modernized grind "stock 340"


If I do that, will I also need to put hardened seat valves as well? Or can I leave that alone? I'm not opposed to going a little bigger, but I am daily driving this vehicle and don't want to dump a lot of money into this engine until I'm ready to completely rebuild it.