I personally see it this way: Would is another way of saying "will". Good sushi would make me happy (there is an underlying "if I get it" attached to would). Could is another way of saying "can". Learning something new could make you happy (the underlying vibe here is that there is also a chance it may not). So the difference is "would" will and "could" might. I hope that helps!

What would make him happy? Vs What could make him happy? For the most part, but I think #1 is more common. Also, #1 applies to a lot of situations. Like trying to figure out what would make your dog happy. LOL-- "What could make him love me?" could also apply to a pet. :P