You mentioned that you wanted to avoid the eBay "find and replace" feature, did that extend to the Auctiva Bulk Revise feature?
If we are talking about Active Listings, you can select the listings in question and click 'Bulk Revise'. Select 'Description' as the field to edit, and you should see a standard 'find and replace' text interface.
Unfortunately we don't have an easy feature for the complete elimination or wholesale replacement of a various listing descriptions for Active Listings, which is what it sounds like you want.
Some options you have going forward for Saved Listings are to use item details profiles, but that would override any setting a particular saved listing had in that section, not just the description.
For a new listing you were creating, profiles are a great way to start off with a default description that you can fill in with specifics (assuming you sell a lot of the same type of items). Also you might look into seller details profiles, which let you set up additional sections in a description (Payment, Shipping, About Me, Terms of Sale, and Contact Us).
As a last resort, you could apply profiles with the new descriptions to the Saved Listings corresponding to your current Active Listings and have them closed and reposted. Reposting rather than relisting so they use the base Saved Listings rather than relist with no changes. However that would end up being fairly expensive considering the number of listings you are talking about.
Hopefully something in that rambling response helps. Can't really advise further without specifics, but you might consider creating a support case if you continue to have difficulties.