But raisins are already dried up, aren't they? By comparing dreams to raisins, our speaker perhaps wants to describe them as being small and already pretty withered. By this logic, if you ignore them, then you make them even smaller and more withered.
Or fester like a sore– And then run? (4-5)
Interesting that there's no talk of healing here. In this light, ignored dreams will never heal and go away. They will fester and then bleed like an infected wound.
Does it stink like rotten meat? Or crust and sugar over– like a syrupy sweet? (6-8)
Both of these similes have to do with change, and how food changes when it is not carefully put away or when it is not thrown out at the appropriate time. Does this mean that even when you ignore dreams, they won't let you ignore them? Or does it mean that you either have to get rid of dreams or act on them (deferring is not allowed)?
Maybe it just sags like a heavy load. (9-10)
When things sag it's usually because they've had to support a heavy load for too long. We associate sagging with the passage of time. Whereas meat can go bad in the matter of days, we imagine it takes months or years for things to begin sagging. In this way, our speaker points to the gradual passage of time.
Or does it explode? (11)
What happens when things explode? They change form. They become fragments of a whole.