Robert,
Every imaginable approach will work for you at this stage. Your own suggestion of visual clarity equaling musical clarity is often true.
Here's some tips:
Listen to symphonic literature with the score through both ends of the telescope so to speak. That is, sit back and watch everything go by (perhaps tracking with the elements that the composer is emphasizing such as a melody and how he has managed to draw your attention there.) This cursory approach entrusts the learning process to the subconscious and will prove fruitful all along the way.
Then find a passage of interest to you (which could be two or three measures) and sweat bullets over every note in every instrument while reconstructucting it on the piano, untill you have a total Conscious understanding to where you could explain it to someone else. Try to understand the general intention of the composer in the passage but also try to understand why he might have done something that is not immediately apparent and almost baffles you. That type of detective work can be very rewarding.
All other approaches of score study generally fall somewhere between the first two. Follow one section, such as the strings. First: all strings. Then, follow the upper, then the lower, then notice the viola seems to be married to the upper then the lower. Once you have a handle on what the strings were doing (during say a period in which they were dominating the music) look at what the composer did with other instruments to either blend with or contrast with the strings. When another section (winds for example) are dominating, what are the strings doing? The other permutations in this approach are obvious.
Make mental notes of what unison writing sounds like in each section and what harmonic spreads sound like in each section.What do unison strings sound like against spread harmony in Brass and vice verse. And so on, section by section.
If you a have a MIDI setup you can play around and get immediate feedback on what works. Play a favorite passage from a symphony into a computer sequencer and you will learn a lot.
Don't worry about spending a ton of time on 8 measures or flying through 8 symphonies, you cannot help but absorb. You will also instinctively know what approach to take and when because you will crave what you feel you need at any given time.
Assuming you have at least a basic understanding of composition, all these things will just start showing up in your writing, plus you will know where to look for a certain sound or texture in the literature as well.
Hope that helps a little,
Dave Connor