Hi Stoleman, its true that PE suck to paint is only as strong as the adhesion between the paint and the plastic.
This is OK for tiny parts (nut/bolt heads etc) that will not have any load on them.
For example - white metal wings and end plates common in 1/20 kits will easily fall apart if dropped or handled roughly if glued with superglue (or any other glue) to painted surfaces. Superglue results in a very brittle bond. Araldite or other epoxy type glues are better but need to be applied to bare plastic/metal for best strength. I scrape the paint off joints before gluing.
For small parts I use varnish that will wick in to the gap between the parts as it dries clear, or wood glue such as aliphatic resin also as it dries clear, or as JCH - very thin superglue applied with a fine pin point before joining the parts, it varies with the result I want to achieve.
Malc.