Well, I wouldn't say the magnification possible in digiscoping is really analogous to digital vs. optical zoom.
Regarding your first sentence, there's been the odd lucky time when my digiscoped photos have shown ID features/ring numbers not picked up by others viewing through scopes at the same time, but in general I don't think digiscoping has much real-world potential as a magnification-booster for a scope.
Others might disagree.
David
There was an old adage when digital cameras came onto the marked 10-15 years ago: 'optical zoom over digital zoom = better quality'.
I think that still stands with regard to digiscoping using a camera through a scope, assuming the scope itself is of a high enough quality to deliver sharp images at the highest magnification.
I've personally found that the image from the scope can then be 'boosted' by zooming the magnification of the camera lens. This might be a combination of optically zooming the camera lens further (either compact digital zoom, or more recently, mobile phones with zoom lenses built in) or by cropping the image from the sensor.
The latter is much akin to cropping an image on your computer screen-cropping an already sharp image from a good sensor packed with high quality pixels results in better resolution, but if the original is blurred, you just get bigger blurry pixels (i.e. no gain).
I regularly use my Swaro 80mm scope at full 60x mag, and if I attach a camera and shoot stills, I can probably capture an image that has slightly less resolution than the the scope is able to deliver to my eye.
However, if I use video mode on the camera (my camera, a Canon 600D, has a 3x crop mode in video that can be zoomed to 10x, but probably works best at around 3x) I can probably extract a little more detail still, meaning that it's quite possible to read distant rings on the resulting video clips (when viewed on a bigger screen at home) that I wouldn't have been able to read in the field viewing only with my eyes and the scope. I've found this worked in practise on a number of occasions.
Of course, viewing conditions have got to be excellent, with little or no atmospheric distortion, stable support, no wind etc, and the focus has got to to be critical.
It's worth saying too, that the resulting images won't win any artistic prizes, but at the magnifications involved, this won't come as any great surprise!
One of the reasons I think, why video is sometimes better in this regard, is that there is no vibration from a mechanical shutter when you take the picture (my camera is older, and uses a mechanical shutter for stills) except when you initially activate video mode. Once activated, the video captures rolling footage with no vibration. Even when there is some heat shimmer visible through the scope - and you do often see this on cold days too - especially over water, there will still be moments when the image drifts in and out of focus. Grabs can be extracted from the footage at the best point of focus and can be very useable for reading rings or taking record shots for identifications/rarity submissions etc.
I notice that Poledark has recently posted (while I was typing this) something very similar re using video through a scope, and with significant advances in this area in terms of camera design and functionality, results can only get better and better. Also, many digital cameras are now being made with electronic shutters, meaning that the dreaded vibrations, and resulting soft images! are getting easier and easier to eliminate when taking stills.
It's possible too, to extract 8mp stills from some cameras' video output, without having to upload to your computer, though I'm not sure if this is possible when using the extra magnification in crop mode? The only limit, it seems, to what we can do with technology, is our imagination, and perhaps our ability to learn how to use all of these amazing features!