As far as I know the only part you can really repair with an EVA'd Kerbal are the rover wheels. You can also repack deployed parachutes, and I guess you can have them unpack stowed solar panels (i.e. you could send a manned rescue mission to a probe that you may have forget to deploy the panels on). I don't believe the panels can be repaired yet unfortunately. As you've already pointed out, the repair still really is only partially implemented, and that's saying it generously. I imagine in the future we will have something like a strut gun that will allow Kerbal to add extra struts to docked spacecraft, or fuel lines. As far as simulated damage, things like air/fuel tank leaks, cabin depressurization, engine wear and damage, heat tile damage etc etc, I think that type of stuff may be quite a ways in the future or in the realm of mods.