I am certain that, if the Yeovil to Dorchester stretch was redoubled and an hourly service could reverse at Dorchester or Weymouth for Poole and Bournemouth, then this fast service (with a local one in between from Westbury to Weymouth ) would find demand very readily.
Meanwhile, the newer 16x units coming on stream will be appreciated.
The problem is the journey time of doing Bournemouth to Bath is uncompetitive via Weymouth - and short of spending huge sums on the Yeovil - Weymouth line, that's not going to improve - e.g.
From National Rail - to travel today from Bournemouth - Bath, the quickest journey I could see was 2h 17m changing at Southampton with a 10 min change.
You're then looking at 2h 45m changing at Reading with a c25 min wait at Reading.
The quickest I could see via Weymouth was 3h 05m with a 6 minute wait at Weymouth.
Dorchester is c 10 mins from Weymouth, so a 'reversal' at Dorchester (even if it were possible) would only save 10/15 mins - and I'm not sure there's anywhere convenient to reverse in any case.
This is not dissimilar to the debate on the S&D not so long ago around here, where again, even if it were reinstated (for which I believe Hades will freeze over first) then its journey times will simply never be competitive with the existing routes.
Between Yeovil (popn 45,000) and Weymouth (popn 52,000) the line serves only one place of any size - Dorchester (popn 20,000) - frankly that's not enough to justify redoubling and certainly not when there are other schemes far more deserving of such improvements.