It shouldn't be too hard to replace the cheesey sping clips with some decent binding posts, but it will depend on how they mounted the existing terminals.
If they are molded with a mounting plate as part of the terminals you may have to fabricate a plate of the same outside dimensions and mount the binding posts to that. If the terminals are mounted individually to a plate or terminal cup, you can just replace them. My bet is they are molded into some type of mounting plate/flange and you will need to fabricate a replacement.
Possible materials are PC borad material, aluminum, thin masonite, stiff plastic, etc...
I agree with you, trying to pass much current through this connectors is a loosing proposition.
Mike