KaineZ,
One of the things that I have started doing to speed things up, something JVJ tipped me off to, was the following.
To use this technique, you have to make sure that all of your page image sizes are identical dimensionally. My first operation after scanning raw centerspreads is to crop the individual pages, making rotation adjustments if needed. I take the cover image first, and after using the rectangular selection marquee, then image/crop. I then pull up the image/size box, and note the resultant images pixel dimension. I then set the marquee tool to 'fixed size', and input the pixel dimension from the cover, and save it as a new tool. Then, I use that tool to crop every page, rotating as necessary to end up with separate, uniform page files.
I then take one image, and create all the adjustment layers I like to use ( I use layers for correction, overlay, level adjustment, and color balance), then save a copy of that file as a template. I keep the template file open, and open each of the other pages, one at a time, and drag all of those adjustment layers to the new file (holding the shift key, so that they register correctly), then save and close them.
Now, you have each file, ready to go with all adjustment layers in place. While this is pretty fast, I am confident that if I recorded the process once, an automated routine could be used to copy all the adjustment layers into the files of a directory, using the Photoshops batch processing.
About keeping file sizes small, I am not sure about that. My preference would be to work on the file without file size constraints, and use more compression in your routine to convert the files from photoshop to jpeg format. If you bring down the individual files to ~ 650 - 1000 Kb, the CBZ file is not too large for public consumption. I know there are limits to this compression, but I haven't hit them yet.
That's the essence of what I am doing, but I am continually looking for ways to improve productivity and image quality.