That would still depend on the product being promoted. A host getting 10 clicks from a managed hosting spotlight per month and converting 1 customer would be better off than a host getting 100 clicks and converting 10 budget packages. So it really depends on the package being promoted. If you look at host search you will see they charge double the amount for a dedicated spotlight. That isnt because it gets double the clicks.
Likewise overture has something like 600,000 searches per month on the term web hosting and only 14,000 on the term dedicated server, yet they are getting over double the rate per click on the dedicated server term.
Its all about the service being promoted. So its not possible to give a broad brush approach to spotlights in general.