Are any of the day trips wheel chair accessible?

The ones I was on were not. Even if you could get the wheelchair onto the small bus, the terrain was uneven in a lot of the places, not easily navigable. These are wild places. At Golden Falls for example, the only rest facilities are at the top of a big set of wooden stairs going up a small cliff. Suggest you contact the tour providers directly and see what they say.

Iceland day tours are routinely cancelled due to bad weather. Cloudy , rainy nights cancelled all the northern lights tours when I was there in February, and I had booked an 11 hour day tour of southern I eland that also got cancelled due to stormy weather. Cancellation was done the day before the tour. It is impossible for tour directors to know days or weeks in advance when there will be cloudless skies or no storm activity. Light rain does not cancel a tour.