Would it dilute it too much to reverse at Bodmin General and carry on to Wadebridge?
As someone with a certificate that says I am allowed to operate Bodmin General signalbox...
There's a "king lever" that effectively locks all the points, and switches the line to "one engine in steam" between Bodmin General and Bodmin Parkway. This would be the likely operating mode for a commuter service using a
DMU▸ , so that a signaller wouldn't be needed at antisocial hours. Then, when the signaller turns up, they collect the token from the DMU driver, put the signals back to red, move the king lever back to "normal" (unlocking the points etc), and then revert to the standard heritage operating methods.
So running an out-of-hours service other than a General<->Parkway shuttle requires extra (probably-paid) out-of-hours staff - i.e. a signaller.
Extension beyond Boscarne Junction to Wadebridge has quite a lot of obstacles - not least two level crossings to re-instate on the first mile, one of which is across a road on a 1:10 (or thereabouts) gradient. Because it's been closed to rail for so long, any "grandfather" rights have ceased, and it'll be challenging to get a safety case. Then there's the problem of providing space for the extremely-popular Camel Trail bike route.
I can't say too much at present, but its common knowledge that there are big expansion plans for Bodmin General station. More will be revealed in April/May 2019.
The raffle tickets sent out with the latest issue of the B&W's magazine/newsletter state that the raffle is to raise funds for Bodmin General's second platform. That too will be a signalling "challenge".