I assume the following is an "out of memory" issue, but I'm hoping there is a way around it or some tricks that can be played.

I have files with many (8-20) layers where each layer contains a linked image. The files also have on average 8 additional layers that are used for custom elements and overlays. Long story short, I'm tracing lines from the photos that are vague enough that a human can pick them out but a computer vision algorithm will fail miserably. My problem is that on many of the files, if I zoom past a certain point, sometimes the "photo" layer gets drawn as completely black instead of the image, and/or sometimes the screen becomes completely white where my tool cursor has passed over. If I zoom out one click then it redraws correctly.
Things I'm already doing to try to help:

• each photo is linked instead of embedded
• all non-essential layers are invisible (closed eye in the layer panel)

Are there any setting in Inkscape that would help alleviate this? Is there a way to force a screen redraw? Is there a way (on Windows 7) to let Inkscape use more memory?

Yes, that sounds like you've hit the memory wall. Here's something I wrote a while ago, which contains all kind of tricks for getting around performance issues: viewtopic.php?f=6&t=12160.

I can't remember if this is mentioned in that message, but if you have multiple core processor, you can set Inkscape Preferences > Rendering > Number of Threads, and help a little bit more. Or if it's a desktop computer, maybe you could buy more RAM?

This is new in 0.91 with the new render and I don't understand it very well. But for imported raster images, you can choose how you want them displayed. In Object Properties, the choices are "Optimize Blocky" and "Optimize Speed". I don't clearly understand what they do, except the "blocky" will allow you to see the pixels, as before. But I'll bet 1 or the other of those can help with this. I just don't know which one you need. (Can also choose for newly imported images, at time of import.)

Minimize/maximize will redraw, afaiu. Or scroll away, scroll back. Zoom also triggers a redraw. Unless I don't understand what you're asking.