where Waxoyl gets is bad reputation is people painting over rust with it, thinking it's some kind of rust-curer, rather than preventer ((event hough there are much better products about these days) You can find on many a classic car a lovely layer of old, dry waxoyl, which flakes off, to reveal a floorpan of rot, because the car's started to rust, someone has then 'helpfully' covered it with the waxoyl. All you're doing is covering up the bad bits, painting over the cracks.
It's all on a cost v miles thing. Do you want the car for another few years? If so, then worth spending the money. Even 'bodge' repairs will buy you a bit of time. But just painting over it won't do much/anything, and won't guarantee an MoT pass, either.
They're not rusty cars, and the rear sills and back arches seem the only real areas that 'go', keep on top of them and you're sitting pretty in bodywork terms.