My first trip to Universal was a one day trip in Hollywood. We got there just before lunch and it was packed soon after. We only got to do a few rides because of the long waits. Given all that plus the cost of the tickets for one day being so high, I expected that to be our last trip to Universal ever. It just wasn't fun.
As the kids got older (8 and 10), they had outgrown Disney and really loved the Harry Potter movies. So we decided to go for 4 nights at CB over Spring Break. The crowds were heavy in the afternoons, so we went early, took a break mid-day, and then went back at night. We had a blast and have made two additional trips back.
So my advice for a 1 day trip would be to get to the park 30 minutes before it opens and purchase the Express Pass if it will be a crowded day. If there are more than two in your party, it might be cheaper to rent a room at a Deluxe Hotel to get Express Passes. That would give you a place to park your car and have an afternoon break as a bonus.