Thread Pool Search Size and Query Cache

We use default values for both search size and query cache. Providing we decide to increase the query cache looking to improve search experience, would one recommend to increase the search size of the thread pool as well, please?

We already normally have several tens of searches queued in the thread pool, I wonder if simply increasing the query cache will improve the performance.

I appreciate we can add another node to the cluster, yet implementing it across multiple sites will be a very costly exercise for us at the moment and I am looking for alternative solutions.