Quintuplets of 2-letter syllables! Tricky parsing and kooky definitions! Yes, I had fun with this. I got the idea with 27A: Let someone's father borrow this Arp or that Duchamp? (LENDADADADADA), which is, however, the least successful of the bunch, in my view. I think the fact that "dada" is used as discrete words twice makes it weaker than the others.
Conversely, 46A: Statement from the proud snake as its eggs were hatching? (IAMAMAMAMAMBA) works both from a humor perspective, and also from a cleverness perspective, as the 2-latter syllable "am" flips around between different words, only being discrete in the first instance.
Anyway, I had fun figuring out the phrases, but that's not all that's nice about this grid. The long downs are numerous and quite long. I think it's interesting that SMOKEALARMS (I liked the clue, although the verb to noun switch was not hard to see through (8D: Signals to leave?)) and PHOTOALBUM (this clue I didn't love, and it was equally transparent, although I had to work to figure out the second part of the answer (I tried "booth first (11D: Where to get in your best shots?))) have to have the same frame to work, namely __O__A___M due to the theme answers they each cross.
The same is not true for the other pair of long down answers, NEXTINLINE (very nice clue (29D: Like Charles vis-a-vis Elizabeth)) and SANTAMONICA (clue was completely unhelpful to me (I've never watched "Three's Company" (24D: "Three's Company" setting (are you enjoying all these nested parentheticals? (I'm going to stop now.)))).
There's also HIATUSES, which I had difficulty seeing, because I'd automatically put in AGRo. I see now that's pretty much always going to be incorrect, so maybe I'll change my autopilot on that one. I find it very weird that I couldn't place FINN, even though I felt the quote had to be by Twain. I was stuck on Tom Sawyer. Even after I put it in, I couldn't get the Huck part of it.
1A: Not much, but better than none (SLIM) doesn't seem quite right. I wanted "some", which feels more apt based on the clue to me. The actual answer feels like it needs a reference to "a chance" in order to work. I give it a C-.