I think you can have a very successful day without G+ if you utilize rope drop and park close/ ride during fireworks, especially if it is a longer trip. We went the first full week of March, which was a moderate crowds week, and did not use G+ at all and I felt like we rode around the same number of rides as we did on past trips during the same week when we had fast pass, which we did use to use heavily. We were a little slower this trip because we had to use Riderswitch with our toddler and everything with a toddler just takes a little longer! Disclaimer that we did do an AH event at Magic Kingdom which we used to ride all of the mountains multiple times and an AH event at HS rather than riding any rides there during the day -we planned to do shows only on our HS day ticket and rides during the AH event. We did buy ILL for Guardians at Epcot one day, but got the free virtual pass a second day.
Some examples of how our days went without G+:
One of ourMK days we rope dropped Fantasy Land and we rode everything in Fantasy Land except 7dwarves between 7:30 am early entry and our 10:30 am brunch at Crystal Palace. We arrived at the very back of the rope drop crowd since we weren’t trying to get on 7 dwarves. Everything was very short waits.
Our AK day with a 7:30 am early entry and rope dropping FOP near the front of the crowd, we rode everything except Kali River Rapids (and we used ride switch on FOP and Dinosaur) had QS lunch and watched the Nemo show and left for the day by 2:30 pm, so we had plenty of time to do more if we had chosen to stay longer or return in the evening.
We did Epcot on our arrival evening, we arrived around 6:30 pm, did Spaceship earth, GG with an ILL , got snacks at American Adventure pavilion, got in line for Remy around 20 minutes before the fireworks show and got off in time to see the end of the show as we speed walked back around World Showcase trying to beat the crowds getting out. We had a second Epcot day later so it was helpful to have knocked out both of the new rides this evening.
We generally went back to our resort during the afternoon but if we were in a park during the afternoon we would focus on shows and attractions during that time since ride lines are longest then.