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> Part of me thinks this is, while not bad in intend, bad phrasing
Agreed. As well as not really what the episode is demonstrating. All it really needs is a tweak from a 'do' to a 'don't', though I understand if the show prefers to give positive affirmations rather than advice that can sound like rulegiving: don't assume the worst of your friends and overthink things! However, it does helpfully clarify things by stating that a *good* friend will always have your best interests at heart, which I think can be true, when there's a particularly strong basis of mutual trust. 
> The party music from the Call of the Cutie is once again reused here at Pinkie’s birthday party. If I can get my act well enough together I will try to track these motifs better. Call of Cutie, The Showstoppers (probably most famous use where it was sometimes a defacto secondary theme for the CMC within the fandom.
Personally I primarily remember it as the music that got swapped out for an All Star instrumental in Friendship Is Witchcraft. They kind of hit on something there, there's an interesting similarity of sorts between the two, even if it's perhaps something to do with the synthesizer/production or whatever the music term would be. 
> I spy with my little eye a streetlight, or I guess what maybe more propperly termed street lantern?
Or even streetlamp?
> I wonder, magical, oil, gas, or electric? 
I'm going to immediately suggest gas just because even if another system is available, Equestria is the kind of place where society's priority is placed more on making sure everyone has something relatively unique they can do for society, and lamplighting fits that bill quite nicely. I'm sure there are some parts of Equestria that buck the trend and use a different solution, however.