Any glue works best with a sanded surface, it give it something to grip on to. So yes, you are right in thinking about sanding the glue line on your boat.

Any 2 part adhesive is only as good as the person getting the quantities correct, sp perhaps the previous builder did not get it quite right, as I too have bought a boat and had to replace a few areas of resin bond.

Any house type adhesive should be tested on a piece of space material first, as you quite rightly say, it could damage the hull. I would also read the label too as the majority of glues may be "waterproof" but they will not cope with the long term Immersions given to a model boat and they too will eventually fail.
I do prefer to use Stabilit as there is little chance of getting the mixing quantities wrong with their measuring system, but make sure you mix it well to get all the powder mixed in.
best of luck and dont forget to post some pictures of your rebuild if you wish as no doubts a lot of followers of this site would like to see it to completion.

It was a Billings Kadet purchased on ebay, while I was sanding down the paintwork on the hull and deck they parted from each other. The adhesive used looked like a 2 part epoxy similar to that Stabilit I have since seen in another thread. it was real hard and well stuck to the ply but came away from the hull very easily, I am assuming that was because the hull lip had not been sanded to provide a key.
This will be remedied but I was just unsure if to use it again or if there was something better available.
I thought about useing a building adhesive such as Gripfill but was concerned the solvent would attack the styreen.

2 decent adhesives spring to mind, either UHU plus, or Stabilit express , virtually both the same type of 2 part mix resins, but I find they are the most reliable for bonding anything to plastics and styrene/abs.
Working time is limited to about 5 minutes efore it starts to set, touch dry in 15 minutes, fully dry in 24 hours, after which you could even drill and thread the stuff!