This is definitely a personal choice thing, as you see by reading opinions. Check out what you would do in each and decide if the extra travel is worth it for you.
I have done Vancouver a little, mainly pre- or between cruises. I find it a lovely city. But I often wonder if it is better for living in than visiting. You can bike around Stanley Park and travel to North Vancouver to visit the suspension bridge, shop at Granville Market, visit China Town and the Gaslamp District. There is a neat torch from the Olympics. Float planes take off and land in the bay. A replica of Copenhagen’s Little Mermaid statue is off Stanley park’s shore. International food. Tim Horton’s coffee and doughnuts. Poutine. Japa dogs. (The Sea to Sky route from Vancouver to Whistler looks lovely, too.)
Here was one quick post-cruise itinerary we did (After a South-bound cruise that started with a flight to- and overnight stay in- Anchorage.):
Disembarkation Day. Off the boat. Taxi to bus terminal. Bus ride to ferry; the bus just drove on (I was not expecting that.). Bus to downtown Victoria. Hotel check-in (The Empress; 150th anniversary of Victoria with commensurate room rate. Hotels are not cheap here.). Bus to Butchart Gardens. End of Rose season with the scent filling the air. Dinner downtown.
Disembarkation Day +1. hydrofoil to Seattle. Hotel check-in. Space Needle and Dale Chihuly museum. Pike Place Market.
Disembarkation Day +2. Lightrail to SeaTac for flight home. Airfares so much better than Vancouver.
It was a lot of forms of travel. Not necessarily a lot of time; but definitely more than just staying in Vancouver.
We came up with this itinerary to save on airfare and do a bunch of things we would enjoy. I was traveling with a 19 yo who enjoys taking beautiful photos. And enjoys cruising, especially to AK (she repeated her Disney AK for her honeymoon - not the above-mentioned one; that was Princess.)
I say have fun with it. Vancouver, Victoria, and Seattle are all easy to visit destinations.