Everybody loves a good quote, and Publilius Syrus was full of them. This one: LET A FOOL / HOLD HIS TONGUE / AND HE WILL PASS / FOR A SAGE is a classic. I'm sure that the version I'm more familiar with, "Better to keep your mouth shut and be thought a fool, than to speak up and remove all doubt," is derived from the Latin original. And added to this fine quote is an eight-step word ladder changing "fool" to "sage." Very nice. I give the theme a hearty thumbs up!
So with all that going on, how does the rest hold up? It's a slow start at 1A: Flexible, electrically speaking (ACDC) (C+), and GPS (5A: "Calculating" device) is no better, but things pick up over in the NE, where KODIAK (16A: Alaskan grizzly) and MONOLITH (9D: Easter Island statue, e.g.) are highlights.
I've never heard the given definition of TOUT (31D: Offerer of hot tips) before, and RIAA (51D: Antipiracy org.) seems like a tough acronym for a Wednesday, but SEXSELLS (40D: Advertising truism) came immediately, and I enjoyed the clue for DUELS (39A: Drawing contests?).
Down in the SE we come to YEOW crossing EWW next to GOO, and although the doubled "OW" looks interesting, but it also highlights what I think was the weaker part of this grid - too much weird stuff like ITD, OOP, OHOH, TIA, and KOA, not enough MAUS, CHAOS, and PAELLA. Still, the quote and the word ladder is a lot of theme, and it was good theme, so let's say this still comes out just slightly ahead.