Despite its potential to improve search effectiveness, previous research has shown that the uptake of interactive query expansion (IQE) is limited. In this paper, we investigate one method of increasing the uptake of IQE by displaying summary overviews that allow searchers to view the impact of their expansion decisions in real time, engage more with suggested terms, and support them in making good expansion decisions. Results from our user studies show that searchers use system-generated suggested terms more frequently if they know the impact of doing so on their results. We also present evidence that the usefulness of our proposed IQE approach is highest when searchers attempt unfamiliar or difficult information seeking tasks. Overall, our work presents strong evidence that searchers are more likely to engage with suggested terms if they are supported by the search interface.