I think venue is extremely important for a fancy thing. This includes:
*mood lighting and elegant decoration.
*Comfortable seating groups (doesn't have to be a room full of round tables since you're not serving a full meal).
*Easy access to food and drink (several bars and service tables so guests don't have to wait 20 minutes for a drink/stand in line for food.)
*A dimly lit garden walk with a fountain is always a plus for a romantic moment away from the crowd.
*Oh, and a castle setting by the seaside is very important.
I strongly believe that the ambience, such as the first three of the above, sets the mood for a very elegant, comfortable fancy thing. (Okay, I was getting carried away with the last two. Sigh.)
You really can set all of this up in your own back yard. A CW of mine even rented a wooden dance floor that was set up in her back yard for her & her DH's 60th bday party . . . Think of the elegance of the wedding party that was thrown in "Father of the Bride."
I went to a wedding reception where I, and everybody else, was dressed to the 9's. It was in a school gym. Bright lighting, paper table cloths, plastic cups, metal folding chairs, etc. While I still had a great time, simply because of the people that were there, it wasn't the best-ever formal
reception that I've attended.