Ed, you make some excellent points here, and I couldn't agree with you more that there are many, many things that can positively or negatively affect the valuation of any particular business. Yet, even with the four examples that you mention above, there are more variables to be taken into consideration. Perhaps the most important one is the buyer's threshold for risk?
In support of your post, I did want to reiterate a few points mentioned in the guide:
1. The guide is not an "end-all, be-all" for the layperson - whether buyer or seller - to determine an exact value for the business. As the guide points out, it is meant to be a general guide that can help the buyer prepare the Letter of Intent WITH his advisory team. Once the process moves forward from there, a more thorough Due Diligence is performed that can better take into account many of the variables that you do (and don't) mention.
2. The guide points out the potential for error if the process of valuation is undertaken by someone who is not trained - it does recommend engaging a professional.
3. With the understanding that such valuations are best saved for professionals, the guide does seek to share some general wisdom that can assist a potential buyer with determining whether or not to pursue any given business opportunity.
Again, Ed - thanks for sharing your thoughts here. Your feedback will assist us with further improvements!