I used Genie+ for Lightning Lane the other day for my first time. My review is most certainly an outlier from others as I was staying at Saratoga for a few days while meanwhile I live up the street. We actually used the first part of the day as a hotel/pool day, so we didn't get to the park until right before the second Festival of Fantasy around 2:30 and didn't have our first booking until around 3:00 (Little Mermaid), and eventually went on to do Buzz and Space with LL, especially since Space is no longer upcharge (along with the rest of Tomorrowland).
We then used it for Jungle Cruise, Aladdin, Pirates, Big Thunder, and it's a Small World, took a break and skipped the fireworks to eat at The Diamond Horseshoe, which is family style now and if it's open during your trip, I would definitely recommend. We then did Hall of Presidents and finished out the park during the extra hours for resort guests and did Peter Pan, Haunted Mansion, Carousel, Winnie The Pooh, and Seven Dwarves Mine Train.
As for if it was worth it, for me, and my situation, it was. We basically didn't get there until 3pm on a busy day and did everything in the park and always had planned to stay into the extra hours so we didn't have to pay extra for a short wait on SDMT (we walked on in about 5 minutes). For WDW hotel guests, I would say that you should take advantage of the early half hour and extended 2 hours and you may not need it at all. However, it was nice to just be able to show up late, stay late (park was open until 1am) and not have to wait in a significant line all day. Certainly worth $15, but I would never pay extra for the rides.