Which improvement is least likely to provide a significant return on contribution?

The installation of a swimming pool is least likely to provide a significant return on contribution compared to the other options listed. While swimming pools can enhance a property's appeal and potentially attract buyers, they often involve high maintenance costs and may not significantly increase a home's value in relation to their overall installation expense.

In contrast, kitchen remodels, bathroom upgrades, and landscaping improvements typically align more closely with what homebuyers seek. Kitchens and bathrooms are essential areas that can greatly influence purchasing decisions; their upgrades often yield a higher return on investment due to the perceived value they add. Extensive landscaping can enhance curb appeal and create a welcoming environment, further boosting the overall value of the property. Therefore, while each improvement has its merits, the swimming pool stands out as the option that is least likely to provide a strong return on the initial investment made.