Replacing 302 heads with magnum heads

I know the 302 heads are supposed to be pretty good but the magnums appear to be much better in every respect. I know I need to change lifters, pushrods, intake, etc but I'm ok with that. I'm aware of the cracking issues on the magnums as well.

Any reason not to go ahead with this? I already have the magnum heads ready to go onto my pretty healthy 318.

Are the 302s rare/valuable enough to mess around with selling or are they dime a dozen stuff?