I have the same problem as Jordan but I am working with video clips rather than photos. I have about 20 tracks (arranged in a 4 x 4 tiled arrangement) at 15% size, each with multiple different clips on the track but I need to uniformaly zoom into all the tracks back up to 100%.
I have also found that simply exporting the whole sequence as a quicktime video (which I thought was supposed to be virtually lossless?) it loses a huge amount of quality so when I zoom into the 1920 x 1080 file it looks pretty blurry at 100%.
Any tips?