I'm sure the 308's could have been made to last longer (They weren't particularly tatty and I don't remember them being any more likely to break down than any of the other trains when I was using them). The PCT's did stump up quite a bit of dosh for the 333's though, so I doubt it would have been politically possible to move them elsewhere.
Sadly there were no other electrified routes round this way that they could have been moved to, but I'd have been happy with 308s replacing Pacers on local routes round this way if the money could have been found for electrification.
The equivalent slam door stock elsewhere was being withdrawn around the same time though so maybe there was no scope for this...
As I've said before on here, there's a parallel with the BR/ Northern Spirit 308s and the plans for cascaded Thameslink EMUs coming to the Manchester area. BR moved the 308s north (when no longer needed down south) and got a few years use out of them before the business case was made for brand new EMUs. I'd wager that it won't be that long after electrification before new EMUs are bought for the Lancashire routes.
You may be aware that the funding for the 4th carriages was supposed to be provided by WY Metro. However, they ran out of funds after they had been built so there was a risk that the 4th carriages would be put in the storage and the 4 car 321s would have moved off Doncaster routes and possibly the 144s would have stayed more in West Yorkshire, so SYPTE coughed up some funds to prevent that happening.
If SYPTE had any strength then they'd have at least insisted that the Doncaster duties got the 333 (with the 321s being used on the "Shipley" routes). Sadly they don't (and WY Metro got what
they wanted)...