Define "hop onto RotR?" When I most recently visited WDW - to give you a sample- Jungle Cruise was up to a 3-4 hours wait within 5 minutes of MK opening JC does not open early; actually, everyoen was held at the entrance of Adventureland. BTMRR was up to a 40 min wait inside of 10 min of MK opening.
It you are in the front of the crowd, you might get lucky and only wait a short time for Rise. If you are held up at all....just 3-4 minutes could easily = an hour for Rise or longer. When I tried to enter HS, my magic band did not work, and I was held up. Under EMH a few minutes didn't matter all that much, now it will.
I can't quite say if G+ is worthwhile for you, but I sorta lean towards saying - if you are thinking to spend $15, Rise - instead of G+ would be a decent option. When you buy an ILL for Rise at 7am -you at least have pretty good odds of actually getting a pass. If you opt to buy G+ and hope to get Slinky- it is a total crap shoot.
If you are lucky, then you get a good G+. If not, your HS day pretty quickly goes downhill.
7am: If you don't get Slinky, your next best option is MF/ToT. If MF/ToT is okay in your book, you can probably at least get that for your first G+.
10:30am: Come 10:30am, Slinky and MF are likely to be sold out. So, you are looking at RNRC, ToT, TSM, or Aliens. MMRR is supposed to revert back to ILL after 8/1, but that might also stay in the G+. You MIGHT get MF.
12:30pm: probably not much left to choose. You might get lucky if it is a slower day.
If you can hop to MK, then you should still be able to get decent options at 12:30 (for after 2pm return).
If do not have G+, watch G+ in June for a very rough idea of the kind of waits you might see. (From 6/2 until 6/30 is roughly the same pricing season as your dates). Just don't assume what you see for G+ in June is what you can actually book though when it comes to G+ passes/return times.
Right now, at 4pm on 5/25: Aliens = 40 min, Meet Olaf = 50min, MMRR = 55min, F= 55min, RNRC= 60, SDD=80min, Rise = 90min TSM= 30min, ToT = 110min.
So is G+ worth $15 - to you - if you get 2 passes that each save about an hour of waiting, plus 1 pass (maybe 2) that save 10-20min in HS?
When we went, the standby waits were all pretty miserable. So as bad as G+ was, no G+ = even more waiting.
But again I say, in Epcot if you aren't doing attractions- you can at least walk the WS/see gardens. In AK, you can always do the animal walk-throughs. In HS, other than attractions, there isn't much to do except maybe the shows.
I will also say, during the extended evening hours just about everything was walk-on. If you can go during those, do. We did more in those 2 hours, hassle-free, than we ever were able to cover during the AM hours - even after jumping through all of WDW's hoops.