A big part of me wants to point out that they invited you, and did not specifcy any clothing style, wear what you want or nothing at all (although nothing at all might get you deported!).

Chance of media being present? Close to zero I would guess.

While I'd expect photographs to be taken, if they are going to be used they will be offical photographers and if they don't want you in the shot, you won't be in the shot.

In terms of simply not wanting to be uncomfortably out of place, just go middle ground.

Personally, I'd expect wine and nibbles from the way you've described it.