I've just seen the credits on Go Vacation (Wii) by collecting all stamps/badges for playing the listed activities once and achieving the specified requirement. Not all activities are listed in this mode, so there are some surprises waiting for me.

My opinion is that this is a really great game, and I say that as somebody who tried it back in the day and didn't like it coming off the back of Wii Sports Resort. Here we are a decade or so later and I have fresh eyes. I found it very enjoyable.

Tons of content, too! I still have so much more to unlock by revisiting the activities and trying to find the hidden things dotted about the island.

For example: Road Racing is one activity and the first time you encounter it you play one circuit race and have to come first. When you revisit it you may be surprised to see there are a further ~25 events: circuit races (road cars, indy cars), checkpoint races (road cars, motorbikes) & slalom races (motorbikes). For the road cars you can pick between compact, sports and exotic cars that all handle differently. This sort of detail applies to each of ~50 activities.

Comparing it to Wii Sports Resort: what this lacks in depth it makes up for in terms of breadth. Don't sleep on it.

Also, fwiw, compared to the Switch version the Wii version features more graphical effects, albeit at a lower resolution of 480p.