Normally you don't ask whether your key has "legal value". You rather ask whether the key of somebody else has legal value, because that somebody else has signed a document but not followed up on his promises, and you want to sue him. That's a generic remark on the legality of digital signatures: if you are in a right frame of mind, you don't want to sign; you want other people to sign the messages they send to you. Because when you sign some document, in a legally binding way, you are really giving away legal weapons targeted at you.
Beyond that it gets complex because law is an area which has been practiced for thousands of years and the complexity has just accumulated since then; and every country has its own system. One big principle of signatures, though, is that your signature is legally binding if it was really produced by you. This looks obvious or even downright silly, but it expresses an important idea: in the eye of the Law, the technical means by which the signature was produced are of secondary importance. It is mostly a matter of burden of proof: if person A sues person B for not fulfilling the terms of a contract allegedly signed by B, is it A who should show elements proving that B really signed the contract, or B who should show elements proving that the so-called signature is fake ? When legal bodies take an interest in cryptographic software, it is mostly to establish on whom the burden of proof will be applied, should litigation occur.
For details in your jurisdiction, consult a lawyer.