Thank you "Down-Under" I think post processing is always going to be required when scanning using this type of technology. And one of the main problems is always going to be the very constrained dynamic range of slide film. To make matters worse, while, with a RAW file shot from life one can always shoot for the shadows (to avoid blown highlights) and then pull the shadow detail up in post for a better contrast result, when scanning a slide using a camera and RAW files this is neve so successful - with slides there is not much shadow detail to be had if it was underexposed when originally captured. Never the less some post processing can improve results of the scan a little in this regard. Personally I do not mind post processing as I like to have control over my files before I save them finally, and in any event I always had to get rid of some dust and scratches - a process which is tedious if in principle simple to do.
I do not know that any modern dedicated digital scanners nor the associated software can improve potential contrast results either as the slides being scanned still have the same deficits - very constrained dynamic range and loss of details in shadows and maybe highlights. Of course, technology does exist to identify and deal with dust and scratches automatically, however. And scanning software will often have a "curves" tool to allow you to manually change contrast settings before scanning.
I do not know if the above helps. But something else I can say is that I did have a plan (too late to help with the sessions already completed) I decided that for any future scanning sessions, I would shoot "tethered" to my PC using Lightroom or another imaging technology so as to be able to better see the scan results instantly on a much larger high-res screen than the small screen on my camera. I figured this would help with assessing contrast outcomes and also sharpness / focus issues. I always found sharpness using a camera to scan to be a bit hit and miss as even using focus peaking, I could not always tell if my files were really going to have the best possible sharpness outcomes. Shooting tethered allows you to see the result instantly (or before taken - not sure of this) to know what you will get and correct it in camera. This might also help fix contrast issues that you mentioned - most modern digital cameras have an inbuilt "Curves" adjustment setting somewhere in their menus allowing you to change highlight/mid-tone/shadow outcomes in-camera.
Usually, no special technology or software is required for tethered shooting if using something like Lightroom, which natively supports shooting tethered. BTW when shooting in this mode as your camera is attached to the bellows/slide holder the exposure time does not much matter - accordingly you can stop the lens down to f11 or f16 (bearing in mind that diffusion may kick in above f11 or thereabouts) and if needed use (say) a 1/8th or even a 1/4 second exposure with no fear of movement blur, especially if you use a 2 second shutter delay when taking the shot (to avoid any finger induced movement when pressing the shutter button). This maximizes the very limited depth of field you would otherwise get with a wider aperture while also keeping the camera's ISO setting to a reasonable level to avoid digital noise problems (though admittedly these are much less of an of an issue with the latest cameras.
An alternative to shooting tethered is to use your digital phone as a monitor for your camera - these can be mounted in the hotshoe of the camera using a mount designed for the purpose (cheap to buy). In this case, the a few minor bits of equipment are needed - a HDMI cable which fits your camera type (they all have HDMI output but often have different HDMI port types) a digital video capture card (these are found cheaply on eBay - about $20) and a suitable USB cable to connect the digital capture card to your smart phone. Plus of course the hot-shoe adapter mentioned above if you wish.) You also need to find a suitable piece of either Apple or Android software to load on your phone which recognizes the incoming signal from your camera. This software can be found free online (or in pay-ware versions which usually have a few more functions such as the ability to fire the shutter remotely) - there are a number of versions. This method works well too but the screen is obviously smaller than the one on your PC if you shoot tethered but has an advantage of being more flexible in that being close to your PC is not needed. But this method does still require you to manually download all files to your PC at the end of the session. I have tested both shooting tethered and shooting with visual output to a phone and confirmed they work. It's a matter of preference which to choose.
