You are looking at in a vacuum. I'm looking at it as for $15 not only am I saving time, I'm also getting many more rides then those in standby. I am that guy that will wave at those in standby.
Are you really getting that many more rides? You can only use LL once per attraction.
With the original paper FP, I could ride many more rides. In fact, I used to be able to hit the headliners in all 4 parks in a single day, most of them with FP and some multiple times with FP. I had to rope drop one park and plan to be there until closing of one of the latest to close but I could do it. Something like that is impossible with this system.
Here's an example of something I would do often. At Epcot, I could rope drop, go straight to Soarin' (when it was over CA without bending buildings), get a FP for 9:30-9:45, ride standby before FP kicked in with a very short wait, go over to TT as soon as my Soarin' window opened, get a FP for somewhere around 11:30. Go back to the Land and get a Blueberry Muffin for breakfast, ride Soarin' with my FP. Ride the rest of the Epcot rides until my TT window opened. Before getting in the FP line, I would check the distribution times for TT FP. If it was for 6:15PM or later, I'd go grab one. If it was earlier, I'd ride with my FP first and then grab one.
Now, I'd leave Epcot, go grab lunch and then head to MK. I'd get a FP for either Space or Splash as soon as I got there (picking the one with the earliest return time) and then go ride the other one with standby. I'd use a combination of FP and standby to ride everything I wanted to do in MK in 3 or 4 hours. Then, I'd head back to Epcot and ride TT with my evening FP.
If Genie+ mimicked the distribution system of the original paper FP then you could ride many more rides in a day if you had a good strategy. You can definitely spend less time in the parks with Genie+ to ride the same number of rides but I'm not sure if you can really ride "many" more given equal time in the park with somebody doing standby only. With ILL added (every time I type that I think of "Licensed to Ill" by the Beastie Boys), you can do more for sure if the standby person is going to ride things like FoP or RotR. You are paying for it but your $24 (I'm assuming that's what it will be on busy days) can save you 2 1/2 hours of standing in line and you can probably ride 3 or 4 other rides in that time.