The bead is likely contained within that 5' minor illusion, but the path it takes to get there can still be seen. This applies whether you took the action to create the Minor Illusion before or after you cast the Delayed Blast Fireball. If no one was there to witness the casting...
Your observations are correct: Illusionist's bracers aren't helpful with minor illusion, except in niche circumstances. Suppose some trigger happy dark wizard counterspells your first minor illusion. This answer argues that it still counts as having cast the spell, so you could still us...
If a creature discerns the illusion for what it is, the illusion becomes faint to the creature. The enemy scrying you will know the illusion is likely to be an illusion, as they see it come into being; they likely know to examine it to see if they can...
If you were in a windowless room with one torch, and you created the illusion of a box around the torch, people couldn't directly see the brightness of the torch, but they could see the fact that the room was still lit by torchlight, and even (with a suitable investigation check) figu...