Possible upgrades to existing subfloor

[raidwi]

Replacing 18mm plywood sub-floor in kitchen due to a leak (was a slow one so went mouldy before it was noticeable).

Whilst it is up, are there any worthwhile upgrades I can make to the existing sub-floor (without pulling up the T&G layer on top of the joists)?

Current structure is as follows:

Floor tiles
2-3mm foam layer (looks similar to this https://www.floordepot.co.uk/item/24041002/vapour-barrier-3mm-foam-underlay)
18mm plywood sheets (each about 1m²)
Tongue & groove plywood very securely nailed to the joists (so much so I'm loathe to pull them up as I'll never get them back as securely and squeak-free).
Joists
Deep cavity

e.g. I'm considering replacing the 2-3mm foam layer with a 2-3mm layer of cork, rubber or Mass Loaded Vinyl on the assumption these will offer better sound and thermal insulation. Which offers the best acoustic & thermal insulation?

 

[Deleted member 174758]

Has your plywood delaminated, bubbled/swelled or started to disintegrate? If not, you probably don't need to rip it out, and even if you do a patch repair, with cleats fixed to the undersides at the joints will do the job