Seems like the rough idle is gone! I need to drive more to confirm, but seems good so far. I replaced the spark plugs, and coated the entire ceramic (white) part of the plugs with a thin layer of the grease (according to the label instructions). The grease I got did not come with a needle head, so I was not able to coat the inside of the coil boots, but I added a small dab at the end of each boot, following Sammk's instructions.
I noticed there were some signs of oil around the engine, so I'll probably replace the valve gasket next time I get in there. Also want to clean up the dust and grease around the engine.