Concerning a possible "most boring preserved line of all" -- am wondering whether any participants here, have ever visited the Lincolnshire Wolds Railway? I have not, and have no plans or wish to; cannot help but regard what I can find out about it, as pointing to its being in assorted aspects, an extremely limited -- and potentially extremely boring -- outfit.
With no first-hand experience of the line: I don't totally rule out the possibility of its being of more interest than would -- as above -- appear likely. This railway is brought to mind here, by a paragraph in Mike Parker's book Map Addict. The section of the book involved, deals with various aspects of the Ordnance Survey map which includes north Lincolnshire -- the author (not a railway enthusiast as such) has not visited the line: but clearly reckons it likely to be an absurdly and despicably petty affair; and uses it, with waspish wit, as an exemplar of many such up and down the country. He writes: "In terms of the map, the fact that these pointless excuses for both railways and tourist attractions are shown with exactly the same symbology as a real railway, connecting real places, is something that pains me to see on a modern OS." While my gut feeling on this, very much aligns with the author's; have also in my head -- in contrast -- the notion that such savage "rubbishing" without having in person visited the thing, is perhaps not altogether appropriate.