I would never recommend buying a system you've never heard in action no matter how great of a bargain you think you are getting. Just be careful not to shake too much or they may be leaving part of their automobiles behind.
I must admit that audio books are one of my current and readily admitted addictions. This way I can make an informed decision without bearing the scars associated with testing an untried product.
Even though you've clung to the past, it has finally met its limitations of usefulness and it is time to move along and embrace the wonderful world of modern technology and what it can mean to you and the time you and your family spend riding in your vehicle. CD/DVD/MP3/WMA/iPod and XM capable though it too doesn't have GPS or navigational assistance.
It is up to you to decide where you want the bulk of your money invested when it comes to technological gadgets and goodies. But hey, that's just me.
It only makes sense that you have good quality equipment upon which to play the music that so greatly enhances and enriches your life. This is probably the best reason on earth to spend the extra money on a professional installation.