AFAIK lounge passes are only good for a single entry so you would not be able to use the same pass the night before then re-use it the next morning. Similarly, you can not use the pass in YEG and then use it again in YVR even though you are on the same itinerary.

YVR lounges have just been remodeled. Should be nice but can't say what the new layout looks like.

There is a nice Fairmont Hotel in the airport (prices vary depending on the date from reasonable to ridiculous). If you are on a budget, lots of hotel choices with shuttle service nearby. You could also stay at a downtown hotel and enjoy a night on the town. Take the new Skytrain if you're going downtown.