The Grouse Grind plays into the widely-held idea in Vancouver that it is critical to be as in-shape as possible, and that you should spend as much time outside as possible. It is a huge challenge, and - at the top of the mountain - you can enjoy some awesome views, food and drinks.
If "climb a mountain" is on your bucket list, this is probably one of the more gentle mountains in the area to climb. You can also do it in 2 hours (max). The views at the top are priceless- you can see all of metro Vancouver on a clear day.
If you hike up, you need to pay for the gondola down (which is around $10). However, if you just take the gondola, it's $40 for a round trip.