What actually makes stitched liquid look wet - thread choice or shading?

I'm firmly in the stitch direction camp. I did a honey jar piece on navy a couple years back and stripey highlights were my exact problem too, and what fixed it for me was switching the highlights from long and short to short satin stitches worked tight and packed, all running the same direction as the flow of the liquid. When the highlight stitches follow the direction the drip is moving, your eye reads it as reflection instead of a stripe laid on top. The other thing that helped was contrast. Glossy stuff has hard edges to the shine, not soft blended ones. I was feathering everything out like fur, which is right for animals but wrong for liquid. On my caramel-colored areas I kept the blend soft, but where the light hit I let the palest cream sit as a small hard shape with an abrupt edge to the mid-gold next to it. That hard edge is most of the wet look honestly. I tried adding a shiny thread once, a single strand of an old silk I had in the stash, and it went glittery on me just like you describe. Never went back. If anything, a slightly duller matte floss with strong value contrast reads more wet than actual shine does, because real caramel is reflecting the scene around it, not sparkling. I'd try dropping the number of strands down to one in the highlight zones too, so the shine shapes stay small and precise instead of blobby.

I land in a third spot that nobody's quite hit yet, wich is that wet shine is mostly about hard edges between values, not smooth blending at all. I did a red wine pour on dark plum fabric last year and made the same mistake, blending five shades of burgundy and it read as velvet, not liquid. What finally sold it was pulling back to basicly two tones with a gap between them. I left a thin line of the dark fabric showing between my deepest shadow and my brightest highlight, no transitional color at all, and suddenly the surface looked glossy from across the room. Caramel on charcoal is actually a great setup for this because dark linen can do the same job as that gap. Try stopping your deep amber cleanly and letting the fabric sit untouched for a couple millimeters before your cream highlight starts. The abrupt jump in value is what eyes read as a reflection on a wet surface. Soft blends read as matte or soft things like frosting and fabric. I'd also skip the metallic idea entirely. I tried blending in a single strand of Kreinik gold on a beer foam piece and it just looked like glitter sprinkled on top, exactly the problem you described. Real sheen comes from the value structure. Also worth trying a rayon instead of cotton for the highlight band, it has a geniune sheen that catches light without reading sparkly.

Adding to the color side, one thing that sold my ice cream sauce piece was putting tiny flecks of the background charcoal into the caramel itself. Real drips pick up what's around them, so every few stitches I'd work in a little of the linen color and it started looking like a reflection instead of a painted stripe. Also, squint at it from across the room before you keep going. If the highlight shapes vanish when you squint they're too subtle, and if they scream they're too hard. It's dumb but it catches that stripey effect way faster than standing close does. Curious if your puddle's getting any of that treatment too, since a pour like that usally reflects in the pool below.

I can't get behind the same direction as the flow part. I did a pour shot on a coffee piece and when I ran my highlight stitches down the length of the drip it just stretched the shine out and made it look like a painted stripe again, same problem as the long and short. What worked was crossing the flow, short stitches perpendicular to the drip, because that's how light actually sits on a curved surface, broken up across it. The shape and size of the highlight did way more for me than direction ever did. Has anyone else found the direction thing depends on how fat the drip is?

For me the turning point on a syrup-with-pancakes piece wasn't thread at all, it was a cheap laying tool. My satin stitches were sitting slightly twisted no matter how careful I was, and that little bit of twist was scattering the light and killing the gloss. Once I started laying every strand flat, the same floss I'd been using all along suddenly looked wet. Twist reads as fuzz from a distance, flat reads as glass. Might be worth checking a magnified photo of your highlights to see if your strands are sitting parallel or fighting each other before you change anything else.

The shape of the highlights matters as much as anything else. On my maple syrup pour I made every highlight a plump comma or teardrop following the curve of the surface, never a straight line, and that did more than any thread choice. Straight highlight shapes are what read as stripes from across the room. Curved ones read as light pooling on something round and wet. So look at your drip edges and ask if the shine shapes bulge a little where the liquid swells, becasue real syrup never highlights evenly along its whole length.