Agreed on the 1/2" being fine as it was oem. However, just a thought, a couple of friends have rebuilt theirs using 3/4" AC fir plywood. These are 19' fishing boats. The additional stiffness even though not an aircraft carrier is nice. Plus, the little bit of extra weight ( a disadvantage to some ) seems to settle these boats a little over stock due to the ballast factor. The weight is marginal, but nice in practice. Convinced me! One of them used 3/4" Advantech, heavier still, and I love the boat now, but I think I'll still use 3/4" AC fir in my Holiday 186. I think the Advantech will be great until it isn't, and then it will be a sudden disaster! IMHO.
On the other hand the Advantech floor is covered in pebble vinyl (nautiliex) and seems fine. The 3/4 AC floor was rolled with bedliner. Tis ugly, rough, and peeling, and the plywood is softening in spots. Plus pressure washing creates peeling. Convinces me nautiliex is a good idea too. Loving your project!