IF it's trademark or aging link traffic then some will pay 6-18 months of revenue, but the trademark market is problematic for buyers in countries with stronger trademark enforcement AND parking companies that accept such traffic are in line for lobotomies.
Valuation is an art, particularly in niche areas where few domains have sold previously. DNJournal keeps stats on current sale prices. The weekly sales totals are not as important as YTD.
Upper valuations for high-priced sites are no longer being considered part of the secondary domain market. Traditional online property managers are no longer able to afford to particpate in high end buys.