Your cracked boulders aren't all that uncommon... Starship Fantasy will run more repros at some point. Or, you might be able to snag some from eBay.
You might want to pull the backglass and take some photos of the batteries... if I were a buyer, I'd be really interested to see what's going on there, especially since you've had the game for 20 years and you're a novice. Maybe lift the playfield (remove balls first) and photo inside playfield... also photo backside of the cabinet head.
I do believe you're sitting on a game that will sell in the 4.5-5-ish range. Playfield and cabinet looks nice.
Don't let the price police jump on you too much, you did list as OBO. You're just going to have to wait and see what kind of offers your receive.
White Water is a very popular title... but summer time plus the expense of new available titles might make the process a little slow. Be patient.