Soft floor...How bad?

OK, more questions from a newbie.

I'm looking at a 1988 V20 CC, owner admits it has a 6x12inch soft spot in the floor, in front of the console.

Question is....

Is this a warning flag for more damage, if this spot is soft will the rest of the floor likely follow. Or do you think a local area repair should be enough.

My logic (and limited fiberglass knowledge) would make me think if part of the floor is soft, there must be a reason and the rest of the floor should now be suspect?

What do ya think V20 guru's..............