The best thing to do when trying to gauge a player's value in a trade is to look at similar examples from the past. In this case, Brad Richards and Dany Heatley.
Richards (27 yo when he was traded) fetched:
-Mike Smith
-Jeff Halpern
-Jussi Jokinen
-4th rounder
Heatley (28 yo when he was traded) fetched:
-Milan Michalek
-Jonathan Cheechoo
-2nd rounder
Nash (27 yo this year) will probably fetch:
-a young non-blue chip goalie with starter potential
-a young forward who can score 20+ goals
-salary dump
-non-1st round draft pick
Examples:
[CBJ/STL] Nash for Stewart, Halak, Colaiacovo and a 3rd
[CBJ/BUF] Nash for Stafford, Enroth, Boyes and a 2nd
[CBJ/TOR] Nash for Kulemin, Gustavsson, Lombardi and a 3rd
[CBJ/WSH] Nash for Brouwer, Neuvirth, Hamrlik and a 2nd
[CBJ/PHI] Nash for van Riemsdyk, Bobrovsky, Shelley and a 3rd