Do you have a reputable local music store? They should be able to give you a valid appraisal. I would be hesitant to use someplace like Guitar Center, or a pawn shop. You might also contact a dealer who sells Heritage, like Chicago Music Exchange or Daves. They should have a better idea about special models like the 20th Anniv and the 357. You don't want trade in value, you want replacement value. Some shops might look at unusual guitars and price them as standard instruments. Pull out a picture of a Knaggs, and he says "looks like a Strat.... $1500" when replacing it might be 4 or 5 thousand.
Having a significant investment in guitars means it's prudent to have a rider, spelling out exactly what instruments you have, including model serial numbers and pictures. A standard homeowners policy probably will have a limit of a few thousand dollars. Having a dozen guitars which are worth $2-3000 a pop means it could be a significant loss. With the way guitar prices have risen in the past 5 years, that guitar you picked up for $1000 might take twice that to replace today.