Hi welcome to the LS430 club! The audio issue was one I ran into as well. I didnt replace but augment. I went with a relatively inexpensive solution by purchasing an android based system from Grom Audio called V-Line. It allows you to bluetooth your audio from your phone or use Google play common apps and run it thru the player. I put my Spotify on it and use my phone as a hotspot. I found that the sound quality is the best when I do that instead of bluetooth. It is a decent way of updating an aging car and it suits my needs. As far as mechanical things to watch for most people mention the lower control arms, if you have the air suspension youll have to decide if you are going to fix it or go the traditional suspension route, and some talk about the transmission having problems (I have yet to experience that though..I have 123k on my 2006). Hope that helps.
