As long as it has good depth and sensitivity, you don't need any bells and whistles. All of those who have machines that double mine in price that I have hunted with, I have out-performed. Like it was said earlier, A metal detector is an extension of yourself. It's performance all depends on the user.
Not entirely true. Good depth and sensitivity CAN be improved with these so called "bells and Whistles." Experience will account for success more than the detector itself. IF you have been "using the same machine for 15 years" and you are comparing your detector to someone who has not had theirs as long, you haven't learned much. Put that 15 year old detector up against someone with the same experience on a high end machine, and I think you'll find why "bells and whistles" make a difference.
Yes performance depends often depends on the user, but given 2 users with the same experience, and the better detector WILL rise to the top.