We just returned on Saturday from 8 days in the parks. Due to the FP+ availability later in the day, we really didn't bother to park hop, even though we had hopper tickets. It was more sensible to just keep getting FP's for the park we were already in, rather than risk the next park having nothing. Sometimes we got lucky. On a SWW friday we had TSMM, TOT and Star Tours (SWW the only time ST kinda gets busy). We finished those up by 2pm and scored a RNR FP for 230. That I believe was luck of someone cancelling at the time we were booking. But that one still had plenty of times open at 2pm. We then got another TOT and RNR after those. Other nights in other parks we weren't able to get some of the E rides at a 4th or 5th FP until later in the night. But we are a close the park family...so it was OK. Except for Space Mt and 7DMT, nothing at MK was much over 10 minutes after 10pm anyway. On 6/13..our last full day, it rained like crazy most of the early afternoon. TT was down all morning and MS was struck by lightening, giving us 2 "recovery" FP's to use. We used our 3rd FP on SE and were able to get a 4th for Soaring at 230 for 545pm. Plus had our 2 open FP's which we used to ride TT twice. So I'd believe the weather contributes to what's open too. Lots of folks do leave when it rains.
We only park hopped 2 times. One day because I booked our SW breakfast on the day we were going to Epcot. We slept in a bit, went to the breakfast at the last seating, then hopped to Epcot and used the FP's I book for the afternoon/evening. I didn't want to spend time during the day we were doing other SW stuff to eat. The only other time we hopped, we did so only because the night we stayed at DHS, it rained out F!. We left Epcot after Illuminations to hurry to DHS to catch the 1030 show. If we had seen it the before, we would have just stayed in Epcot.
Until WDW lets you pre-book FP+ in more than 1 park, or lets you book a 4th, etc... on your phone, I don't think I'd waste my money on the hopper option on future trips. But I would say, IMHO...book the FP's for the park you are going to 2nd. Get the rides in standby in the first park, do what you want to get done, leave....then relax at the 2nd parking knowing you are getting in the 3 attractions you booked. We spent 2 days at each park, so we didn't feel the need to have to leave to fit in something we missed the first day in that park. We just saved it for the 2nd. But for a shorter trip, I can see it.
regards