For most people the 12 free pics is enough. Some don't even use all those, and the pics they do publish are so amateurish it's a wonder they ever sell their items.
I use the 12 free and up to 20 within the text as html inserts. That 20 would include the 12 free ones, so another 8 pics not shown in the regular eBay area.
IMO, the pics within the description are what sells the item. They are larger and I can put appropriate comments below the pics to explain the item. I can also circle some aspect in red pointing out a bonus aspect or a "wart"
Pictures within listings actually harms you search wise though not terribly so I guess you have to make a decision is having good pics with descriptions worth a bit of a knock in the search dept?
Not criticizing you I'm running into the same thing and have chosen to harm myself a bit in search for a more professional presentation and more informative listings. What mine is in reference to is using templates. This is incredibtly stupid since ebay themself provides templates but ebay uses the fist 150 words of your title as the main determining factor in ebay search algorithm. If you have plain text your first words are probably 1 Ounce Silver American Eagle Coins MS89 US Mint etc, etc, etc. Basically all relvent stuff. If your using a template on the other hand your first 150 characters are going to be nothing but <dsfdsasdfd3483743843> and basically just HTML code so I'm not showing up the best I can. I've heard this directly from ebay reps and other big time sellers so I believe it to be true.
Now in my case I find most people are using templates in my category so most other big sellers aren't getting an advantage over me. I rank pretty well in search so dont think its affecting me that much and more importantly I've decided that having a professional presentation and well laid out description and pics outweighs any minor knock in search I may get for doing things with a template.