ignition systems

Are ignition systems worth buying, such as msd?

If you're trying to squeeze every ounce of power from your engine or are running a turbo or surpercharger, then yes.

You won't notice a difference unless you mess with your compression, lift/duration (cams), fuel system... then maybe you'll get an additional 5 ponies for a full ignition system. IMO it's worth it at that point, when your struggling for every ounce of power.