This is why I personally prefer to take a steer from the RUSs or Route Studies (the new terminology). As per your example it is fairly clear from the latest Wessex route study (in draft) that the NR preference is just as you suggest, for more main line trains to places such as Southampton or Portsmouth etc.
Personally I think that the proposal in my example has no merit until such time as there are more paths. However I also think that more paths are likely to be used up by an increase in passenger numbers from other locations by the time they are available, resulting in the proposal being unlikely to go ahead.
Having said that, if Crossrail 2 is built (likely given my reading of the route study), there could be an argument to extend Crossrail 2 services from Working to Camberley as some of the dis-benefit from the longer journey times would be offset by the improvement in journey times to central London stations along the core.
Although I also think it is a lot of money to spend to improve services to two stations which contribute less than 750,000 passengers to the network (I know that passenger numbers are likely to go up if the link was provided, but not by much), so is unlikely to be justifiable.
IF you were to spend money to provide a junction (full grade separated) there a west facing junction would likely bring more benefits. Although it wouldn't bring the same level of journey time improvements to London from Camberley it would reduce a bit by changing trains at Farnborough Main (which could be one of the locations which sees improved train frequencies when more paths are available). In addition, such a junction would also provide a more frequent to the stations service between Basingstoke and Farnborough (including Hook which on its own has more passengers than Camberley and Frimley combined, and Whinchfield which is likely to see several thousand new homes built in the coming decades which is therefore likely to see a lot more passengers added to the network than Camberley and Frimley would add if the east bound junction was provided, especially as many of the extra passengers at Camberley would likely to be people who currently drive elsewhere to then catch the train).
However even that is unlikely to be built any time soon, if at all.