You may be right about the power of any conventional explosives in the 'case, and even if it was a dud, it would amount to a dirty bomb, but that's assuming everything else inside the bomb was functioning, and as post 42 points out, the electronics are just as vulnerable to deterioration. A suitcase nuke can't live long without regular returns to a lab.
Weapon core stored at site A, electronics package at site B. Wow, that was a tough one to solve.
You are forgetting that these are designed as infiltration devices, not "flight line" ready.