First of all, I have to say that registering on a forum to ask that question was fantastic on your part. Most people in your shoes would probably end up selling the car cheaper or trading it in to a dealer and getting ripped off. (never trade to a dealer unless you have a POS)
I must ask you though, what kind of car would you replace this LS430 with? Are you bored or tired of this car? If you are happy with the car then keep it by all means.
I still believe a used LS430 is more reliable than most other NEWER luxury car brands or even other cars that aren't even considered luxury cars. The LS is simply built to last. All you need to worry about is changing your oil and routine maintenance as with any other car. When something does go wrong it'll likely be something that's BS (like the telescopic steering motor that stops working) that you can do yourself or bring to your mechanic. I know what you're thinking, you don't want to be caught dead stranded in a questionable area when your old car breaks down. I wouldn't worry about the LS leaving me stranded unless I didn't keep maintenance up to date.
If you decide to keep it, for your peace of mind you could replace the timing belt/water pump/tensioner. Spark plugs, drive belt, and the other fluids. It likely DOESN'T need these at all at those low miles. Just make sure you change your oil with a good synthetic brand every six months or 7500 miles for good measure. If you have the air suspension that is also an area of concern but it's simple to switch over to the conventional springs when that day comes.
Now.. to answer your questions... At that mileage KBB rates the value at $22k in excellent condition depending on options. I personally think the car is even more desirable than other LS430s because of the extremely low mileage.. so I'd ask for 23k-25k if I was to list it for sale. You can try listing it on Autotrader or craigslist. But knowing that this car is capable of easily going half a million miles without major work (yes 500k miles, anyone here would vouch for that) I wouldn't sell it.
In a nutshell, like the others have said, just enjoy the car and don't worry.
AAAND lastly, welcome to the single life!