2011 328i xDrive 6MT with 119,000 miles. Bought car 2 years ago with 112,000 miles. Runs good. Depending on what you read it looks like plugs should be replaced every 60,000 miles? If so, I'm coming due. Wondering if preventative replacement of ignition coils when I do the plugs is a good idea or a waste of money? And, are the Bavarian Autosport "High-Performance Ignition Coils" a good idea? Coils for this car range from BAV standard coils at $18 each to BAV High Perf. coils at $45 each to BMW OEM at $82 each. Thanks!