I never gave lightning much thought, even though our house is one of the highest in the neighborhood.  That is, until we installed a metal chimney cap.  We had to put one on, since rainwater was causing the lining of our chimney to deteriorate.

Anyhow, now this shiny metal (aluminum, I think) cap adds an extra foot or more to the height of the house and I'm worried lighting will hit it.

Would painting the cap or coating it with tar or rubber help?  Or somehow insulating the cap from where it contacts the chimney itself?  I don't think running a grounding wire is very practical  –– at the very least it would be very unsightly.

When I was a little kid lighting struck our chimney.  It had a metal cap and a chain to run the cleaning brush up and down.  The bolt hit the cinderblocks, knocking a good chunk out of them, traveled down the chain, fusing the links together, somehow jumped in the wall of the house and blew out an outlet in the basement and scorched the wall.  I mean literally blew out.

Point being the metal cap didn't get struck, the blocks took the first hit.

If you are worried about it Put up a spline ball.





This is what we use on our towers.





http://lecglobal.com/lightning-solutions/protection/spline-ball-terminal-sbt.html

 

Painting won't help.

Is the cap connected to the metal liner inside the chimney?

Without an electrical connection to ground, it isn't any more likely to be hit by lightening than the brick is.

Have you ever seen (heard/felt) a close strike?

I would have a lightning rod or spline ball and grounding cable put up sooner rather than later.

It's ugly, but I bet it works a lot better than one of the classic looking ones.  I like the look of the old ones with glass globes:

No metal liner.  It is connected to the terra cotta flue, which sticks up about 6 inches higher than the brick chimney.