I'm not inclined to think there is no specific 'rule of thumb' on the percentage change of value governed by the number of foreclosed property in your or any given area. Percentage rules seldom give credit for area, terms or condition. Saying that your property is worth more or less due to a percentage specific can not be correct due to the number of foreclosures. What counts is what those properties ultimately sell for.
That being said, if several properties that are substantially alike sell for a price that is below what used to be your price median, In terms of appraisal you will suffer a loss in equity.
It is no secret that appraisers have become more scrutinized. They are under considerable pressure to accurately price homes. Market data is public record post sale and we all must deal with the fact that Banks are willing to sell foreclosed and REO property at a loss. This affects the comparative value of every home in a specific market place.
I suggest you deal with professionals that are consistant and knowledgeable in your market. Getting a competant Realtor is always a favorable first move.
Buffalo Grove, IL 60089