As far as the existing replacement foam, EPS, goes, its very similar (exactly the same?) to what SC used originally, and styro cooolers. If you're confident it's in good shape, and was well done, you could leave it, and be diligent w/ the care, maintenance and storage of the boat. You'll start to notice styro beads in the bilge when there's a problem w/ the EPS.
If you pull the deck and reuse it after re-doing the foam, I suspect you could hit some of the previous rivet holes you'd be drilling the rivets out of. Not knowing how well the below decks was packed w/ EPS and how diligent the PO was in keeping the stringers and structure aligned when he installed the deck, I don't know if you'd be able to hit 50%, 75% or 95% of those previous rivet holes. Once you pull the deck and start replacing the EPS w/ XPS, some of that stuff might move around a bit. And for re-riveting work, it doesn't take much change for mis-alignment to occur.
For sure I'd reserve pool noodles for at anchor swimming and ABOVE deck added foam filling of nooks and crannies, but not for use below decks.
BTW: I use sections of pool noodle along the top of my windshield, tarp support structure and boat cleats while the boats are under cover, so although 100qty is a BUNCH, you might find other uses for them.... Got a spare 18V or 24V cordless drill and NEED a trolling motor?
