Well it won’t be optimal, but yes, I think doing your zooms of AVCHD footage in post is a better idea. My reasoning is based on the fact that digital zooms in flip type cameras give up pixels to create the zoom, so your image is made up of fewer but larger pixels.
If you transcode the footage into a good high def format like prores, you haven’t created any more pixels than you had in the camera, but the quality of the blow-up is going to be better than what the flip could do in real time. Also, you have the option of applying various upscaling plug-ins to size-up the footge by interpolating what data you DO have in the image, in a more controllable way than what the digital zoom inthe flip can do. Then too, adjusting the luminance channel sharpness in post will add to the *perception* of more sharpness. So, you just have more abd better tools in post to do a blow-up, than if you do that in the camera.
The flip type camera is really meant for wide shots and stuff that is within arm’s length, not for telephoto work. Same for it’s audio abilities.