Really,the only things wrong with the 150s are the appalling window arrangement which doesn't suit
any seating layout (the SR PEP units set a paradigm which BR couldn't break out of until the advent of plug doors on the Networkers/Turbos etc.) and inadequate/lack of underfloor acoustic insulation. They got a bad rap in the 1980s because of usage on long-distance services, for which they were totally unsuitable, until the 158s came along. Otherwise, they're solid, reliable commuter units which have certainly proved their worth (I know because I used them for that purpose for a few years!).
I do feel that 150 001 should go into the National Collection when withdrawn (150 002 has been too heavily butchered in its time) because it was the prototype for the highly successful 'Sprinter concept' - every vehicle has a single engine - which has only recently been superseded by the new generation of 'electro-diesel' units (or whatever they're called). But I travelled on 001 on the Penistone line last year and oh, how depressing! The first thing I noticed was that it now has a big disabled toilet fitted, but if that's the price to pay for continuing in service, then fair enough. Much, much worse, though, is that the entire interior from waist level upwards - including the aluminium trim strips - has been covered in white slap (think Mr. Bean redecorating his flat by exploding a paint pot with a firework!), which can only make restoration to its original condition more difficult.
I say replace the internal cab door as visually that just shouts 1970s to me!
For me, that's one of the things about the 150s which represents the Darwinian link between 'proper' British rolling stock and the plastic stuff which came afterwards!