Managing the content network can be very time intensive (excluding poor performing sites, targeting highly relevant sites, placements ads…) and you are right that it does take an investment of funds to discover how to make it work for you. If you have a relatively small paid search budget, then participating in the content network may be more work than it is worth.

With the proper analytics in place, you should feel confident in setting a portion of your monthly PPC budget for testing. That testing could be on improving your content network performance and/or testing ad creative… We find that may clients can grow the success of their campaigns substantially when they allocate 10-15% of their monthly media budget to testing (new campaigns, ad creative, content network…) This ultimately leads to a larger and more profitable paid search effort.

I would also like to add to your 2nd point that measuring conversions is essential, but one should be optimizing based on of Margin or ROAS not Cost Per Acquisition (CPA) as CPA doesn’t take into consideration the value of the transaction.