For a first DIY Dynavin takes care of a lot that is on the DIY to do list
1) iPod integration (and the CD Changer before iPods) ,
2) activating aux in
3) hands free cell phone capability. These 3 items alone cost $350 when I did them 2 to 4 years ago.
4) Nav - that was a $2000 item until Dynavin and Dynavin doesn't take up the left side of the trunk.