Do you think having better search functionality in WordPress is worth paying for? Have you installed any plugins or have manually improved the search capabilities on your website?

WordPress' biggest lacking feature till date is an advanced search feature. However, paying for search would largely depend on if you're making enough money from your blogs to justify the extra cost.

Then again if you're a huge blog, "outsourcing" your search requirements makes sense.

I use my own plugin "Better Search" - https://wordpress.org/extend/plugins/better-search/ on my sites which uses mySQL's FULLTEXT index.