Actually, yes it is entirely relevant. We've all seen the wrecks that seem to litter every preserved railway and it's not a good look - it doesn't give a good impression.
Any vehicle at a preserved railway should have a purpose:
1. Operational
2. Restoration - in which case it should have a plan in place for the work to be done with an expected timescale for completion
3. Exhibition - non-operational items that are cosmetically restored as part of an exhibition or similar
4. Parts donor - keep them hidden out of the way as far as possible, but they are needed
Anything else should be binned. I would suggest a loco (or more likely bits that were once a loco) that hasn't had any work done on it in 20/30/40/50 years falls in the "bin" category. It certainly isn't likely to be restored and isn't going to be providing much/anything in the way of parts, either.
(Sighs) yes this is a problem for a lot of lines, however, it can be attributed to the 'ill get round to it eventually' mentality. For example The Bluebell railway has a huge backlog of locos in its workshop that many have taken well over a decade to make progress on and only really in the past couple of years has it had the epiphany of we cant keep hoarding all these locos and now they sold off the USA tank and wouldn't be surprised if a 4mt or the London tank leaves the line in the next 5 years.
In some cases there might actually be a demand to restore a Barry loco but its blocked in the workshops by a slow moving project that isn't great at making efforts to raise funds or gathering attention to their project so its out of the workshops so that the Barry project can move in. Going back to my Bluebell railway example, the 2mt project has barely moved along in 20 years, Stowe should have been done by now if their fundraising campaign was stronger as the Tender was in good condition pre overhaul, and the Primrose project is essentially rebuilding a loco all over again due to how bad the deterioration was on it. Frankly the Fenchurch, Camelot, and Brighton Atlantic project have come across as the most confident there in the past decade and have been successful due to the fact they updated us regularly on its condition and people where confident to give them funds in return.
And for your 3rd argument, yeah i admit its near starting from scratch but if there is demand for new parts for a loco class by many societies they can do them in batches and its an excuse to make them up rather than constant one offs.
In some cases a Barry loco can brighten a heritage railway up if a particular society and line gets it. The KESR is seeing 4253 almost as a silver bullet for the line as it will last longer without needing to take on water when Robertsbridge is done. The Gloswarks fleet these days comprises on seeing barry locos being brought back with P&O line, their 4mt and the 28xx.
In order for a barry scrapyard loco to succeed, here are some good conditions for it to do so.
1.) its at a line that isn't over-saturated by many former big railway locos and its a line that many people have just about heard of in passing. bonus points if most of the current fleet there is mainly industrial tank engines or diesels so the spotlight turns to the Barry Wreck in return to interest enthusiasts.
2.) The society who is restoring the loco is determined to do so and is willing to show up to events such as model railway exhibitions, galas etc etc and posts monthly to keep stakeholders and interested enthusiasts in the know
3.) There is signs of progress being made with the loco with workshop photos, pieces being worked on etc etc.
Thornbury had a good campaign before this summer, and was good at updating us about its progress.