I always wonder why Presenting The Fabulous Ronettes gets almost zero acknowledgements despite it being essentially a prototypical Pet Sounds.
THIS.
I had the exact same reaction when I heard it. What an utterly fantastic album and definitely a blueprint for Pet Sounds. Has Brian ever commented specifically on this album?
Hearing the track for You've Lost that Lovin' Feeling was also an eye-opener in terms of its obvious influence on I Just Wasn't Made for These Times.
I'd say that Brian's work on non-Beach Boys music was more Spector-influenced at first... The Honeys and Girl Group stuff. Even Guess I'm Dumb is more complex than much of what he was doing with the Beach Boys at the time. Much of Today! has pretty sparse-sounding tracks compared to Spector's dense ones, which is why some don't sound as good in the stereo mixes (imo), whereas the ones on Summer Days (and Summer Nights!!) are where he's really taken off with the Wall of Sound. That sparseness contributes to the delicacy that he has compared to the power/anger of Spector. That said, you can definitely see the techniques being learned and applied as he progresses.
It's interesting how Phil kept going with River Deep, Mountain High and Brian started to pare it back with SMiLE (vocal acrobatics not withstanding).