Installing some coilovers, and the lower rear shock mounts have a gap between the shock ears and the control arm (maybe 1-1.5mm). Is this an issue? I'm leaning towards putting a washer in there to take up the space. What do you guys think? Just tighten it down as-is, or add a washer?

http://www.flickr.com/photos/66462178@N04/7256592940/

 

Looks like you got a used set, and a spacer is missing.
Personally I would put a spacer in there to fill the gap. I would not want to bend the shock mounts.

 

Do you ever wash the bottom and wheel wells of your car?

 

Haha. No. In fact I haven't washed the car at all since the clear-coat started peeling around 3 years ago. One of these days I'll have it re-painted... Just a lot of other things to do first.
You should have seen the engine bay and front undercarriage; small oil leaks mixed with road dust turn to very nice sludge.