The Church already is looking into more detailed marriage preparation, which includes filtering out the same reasons for which later nullity decrees are granted. This is what Pope Benedict called for in his
address to the Roman Rota last year and at least where I live, this is being done.
We can’t make people take polygraph but it would be great to make them go point by point through a list of problematic issues, some disqualifying and some “merely” troubling, and, let’s say, confirm with their signature that they’ve read it carefully.
At the same time, preparation procedures cannot violate the dignity of the human person and I have doubts about some of the proposed measures that I hear about (mandatory medical examinations etc.). Marriage prep shouldn’t be turned into a humiliating ordeal. Nupturients shouldn’t be humiliated on the onset of thair marital path.
Also, don’t really see room for a proper contract, except maybe where certain jurisdictions allow spouses to opt for indissoluble or more difficult to dissolve marriages at civil law. Or perhaps some kind of penalty against a non-fault divorce petitioner, although I suspect many courts would regard this as unconscionable.
As for people blindly signing off: well, this can actually be dealt with by a procedural rule: the person administering the document to sign is not to accept a signature placed without reading the document. The signatory would need to flip through the pages and wait out while pretending to be following the lines of text. Pretty hard to do convincingly and extremely boring compared to just reading it.
Another idea is that preparation could include a final exam, actually. Some sort of test that would use plain, normal language and avoid an academic bent.