I kind of go along with what Ben said (in reference to the silver con figures being "useless" when opened). If it's a figure that is in the films in the form it was released as a figure, it gets opened. If it's an EU (in terms of source, such as the Clone repaints) figure, it gets opened.
The only figures I haven't opened in my collection are:
-Celebration III Darth Vader (due to the packaging)
-Lava Reflection Darth Vader (horrible sculpt and more of a novelty)
-Lava Reflection Darth Vader on Mustafar (novelty)
-Lava Reflection Obi-Wan Kenobi on Mustafar (novelty)
-Titanium Series Vintage Finish Boba Fett (novelty)
-Titanium Series Silver Slave I (novelty)
-TSC UGH Scorch (novelty)
-TSC UGH Boba Fett (novelty)
I think that the list above, as you can tell, are based on novelty more than anything else. What use for a loose Lava Reflection Vader would I possibly have in displays? The UGH figures are nothing more than regular figures with a fancy stand when you open them, and one opened Titanium Fett is enough.
That said, you should have seen the looks on people's faces when they've seen Sio Bibble, R2 with Holo Leia, TC-14, R2-B1, etc sitting out loose. "YOU OPENED THEM? WHY?"
So, um, long story short:
-Regular figure that was in the films? OPEN
-Commemorative figure that is superfluous? CARDED