Well, like often, I'm a day late and a dollar short. How did it come out? I make pasta salad often enough in the summer and always make it at least a day before I plan to serve it. I don't care for bottled salad dressing, though, opting instead for olive oil and vinegar.
I would definetely dress it the day before. Some of the liquid will be absorbed into the pasta but not much. Give it a toss before serving it. You'll see then if it needs more dressing or not.
The reason I like to use vinegar instead of bottled dressing is because I like to use different vinegars, like pear or raspberry or tarragon... This way, I can compliment the other ingredients in the salad.
If I wasn't so busy swimming and drinking alcohol to excess this past weekend, I would have noticed this