Re: finished plywood or particleboard floor - opinions, please
You said "mostly sound particleboard". Once wet particleboard and OSB loose there strength very rapidly. If you have weak spots it would be better to replace it. If you do replace it you could then install 3/4" plywood as Canuk described and be done.
I don't know why you were hoping on a reply from Canuk, he thinks a dirt floor with bear grease rubbed on it is an excellent finished floor.
Be sure you live your life, because you are a long time dead.-Scottish Proverb