The following advice is only good for rooted devices.
Have you tried ChainFire3D's night mode? Especially the custom night mode in ChainFire3D Pro might be helpful for customizing colors. For reading, I like green text on a black background. So I set the CF3D nightmode to Green, and then set the ebook reader to white on black. The white then turns green because of the nightmode.
You might also consider my free SuperDim (in Android Market or code.google.com/p/superdim/) which lets you set brightness profiles (coordinates with ChainFire3D's night mode). You could save a profile and quickly switch to it. For instance, on my Archos, I can run SuperDim, and then switch to it from an ebook reader app by holding HOME, choosing SuperDim from the recent apps list, and the go back to the ebook reader with the BACK button.
The AdjBrightness app that you mentioned has an option to lock in the brightness setting? Does that work for you? If it does, I can add a similar option to SuperDim, but the option just didn't work for me, so I didn't bother to include it in SuperDim.