Notwithstanding below, the Reigate to Victoria service sits at Redhill for 6-7 minutes unnecessarily just to allow the platform at Reigate to be cleared, but if the service started at Dorking then maybe this would not be necessary, saving that time on a overall journey.
Even so the current intention is to build a 3rd platform at Reigate so that these trains can be extended, which includes additional power and signalling works. This is moving to detailed design phase now as an enabler for the Croydon CARS works. So its unlikely an extension to Dorking would be considered.
Your post has prompted me to look at the schedules in detail. I hadn't realised quite how messy it is! It all seems to stem from the fact that the electric service to Reigate has gone half hourly when the infrastructure doesn't support it. The Redhill to Reading stopper sits at Reigate for four minutes to avoid a conflict at Redhill. As you have pointed out, the Reigate to Victoria trains sit at Redhill for seven minutes. Even the hourly train from Tonbridge has to wait outside Redhill. The up journey takes 35 minutes which I think is the same as the thumpers in 1993 to 1994. From May 1994 the electrics took 30 minutes.
For the time being it would work better if the XX30 from Reigate reverted to being a through train from Tonbridge. It would depart Tonbridge at XX08 arriving Redhill at XX39. The XX39 from Victoria would run to Tonbridge instead of Reigate. The XX00 from Reigate would depart at XX05. It would have to use platform 0 at Redhill to avoid conflicting with the Gatwick to Reading train. The stopper to Reading could revert to its previous departure time of XX34.