Try idling and putting on your headlights and holding
the stem for your brights back gently so that it puts
on the brights and headlights at the same time and
see what it does to your RPM's. May be a bad ground
or a power issue with the alternator.
If the boots are ripped it's time to replace or rebuild
it. I would suggest replacement since Autozone has
lifetime warranties on CV axles. It rips, you bring it
in, they give you another one.
I wouldnt know what to do about the coilovers.
I'd be hardpressed to believe it'd work with
the Impreza's coilovers though. Have you tried
asking on bbs.LegacyCentral.org?