Oh gosh, as a SFMM regular, the place is safe, clean and has great tasting food. Never had any issues there. Also, the food options have gotten a lot better in the last few years. Heck, they don't offer Chipotle food, or a Captain Kidd's Buffet.
https://www.sixflags.com/magicmountain/food-and-dining
My favorites include the hand battered fish and chips, the chicken wings, tri-tip sandwiches and others, and since I have a meal plan, I basically eat for free while at the park.
Yesterday at Knott's, with my meal plan, I got the Honey Walnut Shrimp from Panda Express and a Flank Steak Sandwich. $27 worth of food, and I pay less than $10 a month for the plan. And since I go once a week, it is great, almost had the holiday Dinner Pizza.
http://www.ocweekly.com/restaurants/slice-of-cheer-knotts-merry-farms-holiday-pizza-8618093
There is plenty to do at USH, in fact for some it is now a two day park, if you watch every show, and visit every major attraction. As for People Watching, have done that multiple times. USH has multiple bars where you can get a cocktail and just relax.