Thanks to all for the advice + suggestions. I've tried out Gorilla Glue as suggested, and found that (as I'd heard before) the glue expands and foams up a lot when it sets - wiping off the foam before the glue sets is a good idea, but even so the joints end up quite messy and I ended up having to use a sharp knife to remove the glue blobs once it had set. It also remains quite rubbery and spongy when fully set.
However, it does "grip" incredibly well - as I found out when I glued a couple of eyebolts in the wrong holes and had to remove them! - and its rubberiness when set should make it very effective for gluing things like mast/sail fittings on sailing models, which are subject to a lot of stress from different directions when the model is on the water (which might eventually weaken and break if a more rigid, brittle glue is used). I've now used it for all of the mast/spar fittings on my 1800s schooner (Bounty conversion).
I don't know how effective it would be for things like prop shafts and rudder tubes, though, as its foamy, spongy consistency when set probably isn't very watertight. I think I'll stick with (pun intended) epoxy for this type of job for now!
I always use superglue/CA (usually the thick "gel" type) for detail work when gluing dissimilar materials together, but I find it's often too brittle for working parts, and also tends to degrade and become more brittle with exposure to water.
I'll definitely also give the Loctite Hysol a try... it's certainly pricey, but not actually much more expensive than good quality 2-part epoxy.
Also thanks to derekwarner for the suggestion of using an O ring or washer to get a neater joint when using epoxy - will definitely try this in future.