Ha! I have the same cup! Bought it from Aliexpress.
My thoughts like yours are that it's a surprisingly decent base to start from but that it's too smooth, too clean and the gold interior is way too "clean and painted on".
My initial plan was to scratch and scrape up the exterior but as you say it's super hard resin and almost impossible to scratch up. One thing I notice in the prop is it has kind of a ridged effect on the outside like it was made on a wood-turning lathe. Ironically it matches up really well to the layer lines you get on a 3d print! So I abandoned my Aliexpress one and started printing one. But I may still play around with my Aliexpress one because it has a really nice heft and weight to it.
To fix this up I would get some sandable wood filler/putty from the hardware store and roughly wipe it over the exterior surface. Let it dry and then sand it up a bit, maybe get a wire brush and scratch some lines and grooves into it to get that wood turned effect. When its dry and has been sanded, wood filler has a pale, dusty look to it which I think would match really well to the dirty dusty effect of the prop.
I would then buy some gold leaf from a craft store and apply that to the interior of the cup, to get that "real gold" look. Rough it up just a little bit to get the worn effect.
The flaking gold leaf on the outside of the prop needs a little work, so use some more gold leaf to make it more realistic. With leafing you basically apply glue to the surface, press on the leaf and rub/burnish it on. It sticks to the glue and peels/flakes off elsewhere so you can control where the leaf sticks by careful glue application.
I'd probably do that and then do a second application of wood filler to dull it down and break up the edges of the leafing a little.
At the end, hit the exterior with a very matt clear coat to protect it, and maybe use a gloss on the inside.
This is inspiring me to take another crack at this myself. I got a really nice print off my FDM printer for it but it's way too light. I glued some fishing sinkers into a hollow in the middle of the stem but it's still not heavy enough. Maybe I'll dig out the Aliexpress grail and try again with that!