tools--->fix power spikes. with my paltry numbers, anything over 1200W is suspect

I had a few of those once. I used the editor to remove them.

I tried this but nothing changed. I even tried lowering the variance down to 10%...

the other thing you could do is export everything as a *.csv file, open it in excel, sort the cells by values of the "power" column from high to low. Anything high would show up.

save it, and then import back into GC

There's a problem when you have a Garmin and start out on a ride before its ready. The timestamps on the records come out wrong and that confuses GC.
GC 2.1 has a fix for it. If you have the .fit files (you should always save them) you can delete those rides in GC and re-import them with 2.1

How do I know when the Garmin is ready? And how do I save the rides as .fit files too???

I guess before it's finished acquiring satellites? The .fit format is the native format on the Garmin's memory - you can copy or move the files from the Garmin to your PC. Are the .fit files information-richer than the .tcx files that connect.garmin.com exports? I've not bothered to save my .fit files thus far, because I figure I still have access to the uploaded files online.

Yes, wait until its acquired satellites. I import the .fit files directly into GC. Going through garmin connect can only lose information, it can't add any.

Or when the override screen pops up.