TrainBrain is correct. The Maryborough service was specifically targetted to provide a commuter timed service from Maryborough, Clunes and Creswick to Ballarat to facilitate access for commuters, students and other to access a whole range of "community" and Government services in Ballarat. The service then running through to Melbourne to provide a day return service. The concept is virtually identical to the Echuca service. No additional rollingstock is technically required as these services are effectively "running on and running off the Ballarat". If you look at a range of other locations in Victoria served by train or coach you'll see from the timetables that there are quite a number of similarly timed trips all intended to facilitate regional commuting to regional Cities.
What is unfortunate and it applies across the public transport sector generally not just in Victoria, is that there has not been the ongoing promotion of the Maryborough service like letterbox dropping timetables, raising community awareness and getting a whole range of community organisations actually organising their activities around the service so that it really is embedded so to speak. Where those things have taken place and the Echuca service is a very good example you will get very good loadings.
Frequency and extra services. There is no doubt that a day return service from Melbourne (like Echuca) on weekends is needed and there is the fleet available for that. I would strengthen that further with at least one mid week trip possibly Wed or Thursday but then fleet availability will be a problem unless those sets can form evening peak trips. RRL may help there because you will get a guaranteed up path from Deer Park in and V'Locities can be turned around quickly. From later this year with the signalling and level crossing upgrades complete between Ballarat and Maryborough, V'Locities are proposed to run at 130km/hr north of Ballarat so a day return service out of Melbourne around 0930 and back to form the evening peak services combined with RRL could be possible.
The stumbling block in this however is funding. Whatever funding V/Line gets it needs to pour into more peak service and so services like this which do have their place will always be ranked lower.