OK, I have a three ideas for you.
Speficially for your 4th of July edition: Sparklers. Have a lightsaber tube emit a lot sparks at the end of it. Obviously it would be a melee weapon as you're using an unlit lightsaber as the base model.
Another idea that you could extend to all of your planned editions: Update the banners and lighted signs throughout the game for each season/holiday. For starters, the Mandalorian banners on Dxun, the ones in the Dantooine Administrator building, all of the electric signage on Nar Shaddaa.
Last idea: For your eventual December Holiday one, why not find royalty free Holiday music and have the bands play it in the various cantinas?
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and help get me some SWTOR referral points!