There's a lot of truth in all that, but all the classic DMU's were bogie vehicles on heavy underframes, hence giving a far better ride than the two-axle "nodding donkeys," even if the 142's suspension was the height of technical achievement at the time!The DMUs which survived to be replaced by Pacers had already been refurbished / life-extended, those that weren't were mainly condemned due to asbestots. Its doubtful whether another life-extension would have been feasible.
But, there's a lot of forgetfulness in this thread. The reality is that by the time the Pacers were introduced the remaining classic DMU fleet were on their last legs. Clapped out suspension, engines which regularly failed and spares that were hard to come by. It wasn't unusual to ride on a set which had a banging engine due to unrepaired head gasket or exhaust manifold leaks. Even more common for some of the engines simply not to run........The upholstery was collapsed - horsehair cushions have a finite life expectation, while the combined efforts of years of cleaners failing to clean had rendered them internally filthy.
The Pacers when introduced were clean, had engines which worked, lights which worked, seats which didn't collapse or leave you covered in diesel fumes, powered doors, were better riding than the classic DMUs, and didn't break down - or at least not until the problems with the SC gearboxes emerged.
In short they were a heck of an improvement on what had gone before.
The problems with the Pacers now boil down to the same problem as with the DMU fleet they replaced: they were kept in service for far too long after they became life expired, in both cases by around 50% longer than the intended service life
Unfortunately the 142s are (and I suspect always were) allocated in areas with a disproportionate amount of jointed track.