I reckon I've found a solution though. If I go down a bit in scale to 1:55, it brings everything down to a manageable size and things which are huge in the larger scale, suddenly look more reasonable, so I'm going to try building a couple of of 1:55 scale models and see how they turn out. 1:55 has been around for a very long time, and is often called "The Ffestiniog Scale" because it started with a series of kits from GEM based on the Ffestiniog and Talyllyn railways.
Once I can play trains on 'Westerooge' I'll make a start on this Rhaetian Bahn-esque motor luggage van, a model I've wanted to make since my first attempts at scratchbuilding in the 1990's. I eventually gave up because it always looked terrible in 1:43 scale when squeezed on to a HO gauge chassis, but when I tried it out in 1:55 I found that it fits rather well. Running on HO track, this would scale up at about 3 feet or 914mm. This is a bit small for metre gauge, but there are a few 900mm gauge railways around Germany, and anyway, I'm not going to worry about it too much- for some reason it bothers me less than tiny wheels.
I've been dithering about this for a while- building 'Westerooge' was partly to gain some experience in 1:43 so I have something to compare the result with (and also as an excuse for procrastination), but I did join the 5,5mm Association a while back, and they haven't thrown me out yet, despite my lack of interest in all things Ffestiniog. They are running a competition to build a micro layout this year, which I may just enter when I come back from the UK...