Although I am not a native English speaker, I feel a major difference between would and could, and will and can. Of course, you will say that would is the past tense of will or that would expresses a polite request. However, the Oxford dictionary also gives those definitions: indicating the consequence of an imagined event or situation; expressing a desire or inclination; expressing a conjecture, opinion, or hope; and expressing a wish or regret. All those definitions express an opinion or describes a situation that may not exist. By the way, when Barack Obama was elected he said, yes we can, not we could.
To me, using would or could is a way to say that there is a risk of failure, and if it does not happen, well, it does not happen, fail, done! Using will or can is a way to say that you will do whatever it takes to make it succeed. It may still fail, but you believe it will succeed. Words are a simple and powerful to express what we believe. We have only one life, and this should be a life of will and can, not a life of would and could. Have a look at where you are and where you want to be, then believe you can, and you will!