the question is whether the price difference is enough to cover the bits & pieces it needs … and whether I’d then have a solid car or further problems might show up in time.
Indeed, that's the big question.
The local one has a long enough MOT to run it for a while and decide if it's a keeper or not, but will certainly need more spent on it if you do keep it, by the sound of it.
The tuning mod's on it aren't really anything special, so I wouldn't let that sway you one way or the other. Silicone hoses and an upgraded dump valve may be nice, but it could be an atmospheric dump valve you hate the noise of and a set of those crappy Chinese hoses that are ready to fall apart.
If it doesn't sell I can go for a look at it with you if you like.
I'd still press the seller for the MOT number though, before even going to look at it.