Yes, I'm sure there'd be a fair amount of demand from both Kirton and Brigg - the 909 bus from the latter always seemed quite well used. Central station's a lot more convenient for the centre of Gainsborough too.
Call me a bit of a dreamer, but I think it'd work reasonably well if the Lincoln - Sheffield services were diverted via Finningley (calling there, of course!) and Doncaster (providing one of the Doncaster - Sheffield stoppers each hour, and also providing a direct link to Meadowhall without the bother of 'combining' services). The stations between Retford and Sheffield could then be served by an hourly Sheffield - Gainsborough Central service (with Central station rebuilt as part of the large shopping development ongoing pretty much next door)...maybe with the odd few continuing to Cleethorpes. Might work anyway!