I agree with JimsCAL - this is an area that I had experience with when I bought my 1966 Nicholson 32 (they are prone to blistering). As I was told by an employee of the boatyard where she was built - "we didn't know how long this plastic stuff would last, and epoxy was very, very cheap - we just kept putting it on until we got bored." The problem is that they were not particularly GOOD epoxies and matts compared to today's. That's why boats of that era really deserve a thorough drying and as many coasts of epoxy treatment as you have time and budget for (my shipwright insists there is nothing gained after 5, but I will probably go 6 or 7 when I redo my boat). Interprotect is well known (it was what was used on mine), but Blake's is also good (now Hempel perhaps), and when I queried around seems to get higher ratings by those that use it. I would also try to get a moisture meter reading on her hull and all appendages - despite being out of the water for a decade, there could still be trapped water in a rudder or somewhere. (Probably not, but if you can do it...).
But I would not increase the hull thickness - you would be adding weight, possibly substantial if you totalled it all up, and it may affect other things such as her balance.