It's all about political capital, isn't it? Ken Skates will be looking at the franchise bid and the South Wales Metro as his opportunity to make a name for himself and position himself as the potential next leader of Welsh Labour. In that sense, it doesn't matter hugely to him if it's a failure long-term. All he needs is for it to look good to strengthen his and the party's popularity up to the next election
The thing is, as you said previously Gareth, it's not just politicians who want something brand new - they're just interpreting the expectations of the voters. South Wales has been neglected, there's absolutely no doubt, and people feel it. We were hit hard by Beeching and the reopenings of the last 30 years have only slightly repaired the damage. Other opportunities to reopen more lines and stations have been missed - my line back home, the Maerdy branch, could easily have been reopened up until 25 years ago, as could the line to Oakdale to serve Blackwood, and they've stalled on reopening to Hirwaun, Abertillery, Beddau and Bedlinog. And of course that's just talking about railways - bus provision has been absolutely slashed, and the rail link buses are gone too
That said, clearly the idea that we should have brand new trains above all else is foolish. While I was frustrated when the initial suggestion of 313s was made, the 323s would be ideal - the sort of trains that with a lick of paint you could pass off as new without the vast majority of customers realising. That's a fleet of 43 3-car trains for the Valleys network - compared to 66 2-car trains and 8 153s now (some of which aren't used on the Valley Lines anyway) you're pretty much at what you'd need
The problem comes with the infrastructure - I think it's inevitable that the Assembly will want some form of wires put up, but someone's got to pay for that. I suspect they'll want to do it as cheaply as possible, and they seem to be won over by the idea that tram extensions and extra stations are cheaper than adding heavy rail extensions and stations. But that's not doing it properly
Anything short of heavy rail electrification is going to be frustrating, but I think Skates and co will think they can con people into thinking something like a tram-train will be an upgrade because it'd be brand new, when it clearly isn't. There's huge political capital in both building something brand new and doing it on a reasonable budget, and that's ultimately what politicians are primarily interested in - not whether or not it'll actually work