I took the time to set up some Unit Tests and set up the targets in XCode, etc., and they're pretty useful for a few classes. However:
I want to test small UI pieces for which I don't want to launch the entire application. There is no concept of pass/fail: I need to "see" the pieces, and I can make dummy instances of all the relevant classes to do this. My question is: how can I set this up in XCode?
I realize I could use another XCode project for each class (or groups of classes), but that seems a bit cumbersome. Another target for each?
Well, you cannot call showing a piece of some GUI a testing even if that GUI is a part of a large application. What you can do here is create a separate executable target and write a small tool that reuses GUI components from your application and shows them to you basing on input parameters. This will eliminate the need for many many different targets.
If you still insist on using unit tests, you can show your GUI for some period of time, for example, 10 seconds. So the test case will run until GUI is closed or timeout elapses and each test will take up to N seconds to execute.