AVE's? You can't even compare ad values between ads. So how can you between ads and pr work? Too many variables. I can't even compare 2 Billboards in the same location with the same traffic (those some media buying companies claim they can tell who sees what). They both will have different visuals and copy. Different brands and different demographic targets.
Value is actually very subjective and can be argued over and over with no winner. A perfect example is stock price valuation. There is only 1 variable. Everything else is concrete. And that variable is the expected growth rate. I might estimate 5% and you estimate 10%. And your estimate might be on a rumor of a new product coming out. Or I might be reading the Economist and seeing that some economic headwinds will hurt the stock.
So measure away. You should measure. And come up with your own values for everything. They don't have to pass muster with anyone but you. I have a rule of thumb for reach. Whether Neilsen or Circulation numbers I discount what is presented based on the fact you can't prove a commercial was seen or an ad viewed. What if you got my brand 2500 mentions online but no one actually read those mentions? What is the value of that?