Yes - peace of mind is the primary reason for me as I'm past dealing with defects and insurance hassles etc as I'm 40+ years old
It definately helps that it's significantly cheaper to perform these tests plus technology has improved and become more available to allow better ECU's etc to assist in tuning when attempting to comply a modified engine (compared to 10 years ago). Ultimately any money spent on engineering HAS to add the the value of the car when compared to similar vehicles which do not comply.
Great story about the Monaro