My general caving attire is synthetic-fiber thigh-length underwear, cheaper heavy cotton work pants, and a cotton long-sleeve t-shirt, and almost knee-high wellies. The wool/wool-blend socks have been a let down - I'll be going back to my usual synthetic-blend socks. I do have a pair of "leggings," and will occasionally throw on a synthetic-fleece pullover. All this works well for dry(ish) caving.
For wattery trips though, I'd like something better. Honestly, I'm just a general wimp, and don't like getting cold. (Heat has never bothered me)
Having never worn neoprene, I'd consider the same synthetic-fiber thigh-length underwear, if it would keep things more comfortable against the skin. I do have some neoprene socks, that I actually haven't tried yet. I guess I could get some cheaper wellies and make drainage holes in them, or perhaps a somewhat durable "swimming" shoe.
If I'm being honest, I much prefer dry-er caving. However one of the caves we frequent has plenty of wet areas, so for those trips, it would be nice to have better options. The famous Scandanavian phrase, "There's no such thing as bad weather, only bad clothes" comes to mind.
(Thank you all for the link to the other thread BTW. I'm probably half-way through it at the moment.)