This would be a great precident too, if the courts could be used to actually force politican to uphold campaign promises.
No, it would lead politicians to give even vaguer statements of their proposed policies than they do now, so as to avoid saying anything that could legally be construed as a promise. It would also probably lead to politicians using more "weasel words", like "I want to cut taxes during my first term in office.' That's not a PROMISE to cut taxes, though it kind of sounds like a promise; it's expressing a DESIRE to cut taxes.
There's also the problem that a person can make a promise that he or she cannot fulfill. For instance, using a US example, if a presidential candidate promised to cut taxes by 50% on every American but Congress laughed in their face after they were elected and proposed such a change to the tax code, could a court force the President to do what he or she does not have the legal authority to do? Sure, the President could ASK Congress but the decision is ultimately up to them. Could the courts force Congress to uphold the presidential candidate's promise? Neither of those seem palatable.