Considering you're looking at a coach that is 20 years old all the stuff the owner listed as installed or options has a minor aspect concerning potential value. You need to look deeper into maintenance. Yearly mileage is just over 3000 miles and there is reoccurring maintenance that is both mileage or time based, which ever happens first. For example going my mileage alone the coach might be on it's sixth oil change and second set of tires but by time the replacements or changes should be much more numerous.
For the price the owner has listed if they don't have ever receipt for anything that was ever performed, changed or touched I wouldn't even consider making a counter offer. There are nine 1998-2000 Dutch Stars with 75,000 miles or less listed on RV Trader with an average price of $29K and a max listed price of $39K so the seller is significantly over priced.
What also turns me away is any time someone lists a coach as a "Dutch Star by Newmar". My first impression when the coach is described as such the seller may not be the owner. Would you ever described you daily driver or grocery getter as an "Accord by Honda" or an "F150 by Ford"? Or maybe it's just me.