This is the perfect opportunity for you to turn that into a party theme. What better party than something that is based upon one of your favorite activities. This also allows you to really customize your party like would not otherwise be possible.
Choose decorations for your party that fit perfectly. For example if you are doing a board game themed party find some pictures of various board games and make copies of the covers to decorate the walls with.
You could also have a ton of games around for people to play. If you are into Star Wars you could pull out your Star Wars collectibles to decorate with for the party. Anything that you already have can be used as long as you place it carefully to maximize the impact of the decorating ideas.
There is no reason you should run out and buy all of your decorations. If you look around your home carefully you may already have plenty of cheap supplies that you can already use especially when you are looking for a creative idea for party themes.
Be creative and imaginative, there is so much you can do to really bring your hobby to life for a party and all without overloading on the decorations. Remember, your party should be fun, but should not consume all of your time to create either.