This is a really good thread and those are very interesting points about maybe the most important overall subject to make your music sound both realistic and expressive. i have also had many problems in this area, and was using altiverb mainly though occassionally Lexicon hardware reverb in a rather complicated way. however, I just started using MIR SE on a not-that-expensive computer (i7 920 with 24 gb ram) and what I am noticing is how it completely changes all of these aspects of the sound, because now the original instruments are placed within an acoustical environment that is completely right for them and based upon orchestral sound instead of generic sound - like Altiverb which is reverb for anything, not purely orchestral instruments. Also, Altiverb is not a mixing environment, just reverb. MIR has completely revolutionized my mixing concepts since it blends together all the elements into one environment and really works. When you can place the instrument in its proper position and image in relation to the others, the other elements of sound - like levels - become so much easier to deal with. An example of this is on a large mix I am doing now, I placed the pipe organ in the very back of the hall as opposed to the front, and this brought out the brass which were a bit overbalanced in one section - WITH NO ADJUSTMENT OF LEVELS. In other words the acoustical environment being right actually did the mixing adjustment automatically. This is exactly what would happen in reality if that organ were in the back (as it of course is) - the sound would be less obtrusive and therefore easier to mix with the brass. Anyway I am noticing how the extreme realism of the overall sound in MIR profoundly affects all the elements of the mix including especially levels. Also, the levels built into the MIR instrument presets are the basically correct real-world levels which give a good starting point.
Anyway on the final level of a CD I agree that you should be very conservative with compression when dealing with orchestral/film music. Hip-hop or other pop stuff can make everything almost one level, but orchestral has to remain extremely wide. I did a CD recently in which I basically did a kind of "manual compression" in which I looked at the loudest tracks and made sure that they were not creating an overall much lower level with a few big peaks that had to be normalized. Just doing that can often bring the entire level up by seveeral decibels without any artificial compression, and it is completely undetectable musically speaking.