Was thinking of a board that could reliably hold strategies for each of the three basic Treasures. Here's my thought:
Beggar, Tunnel, Trader, Coppersmith, Feodum, Counting House, Embassy, Border Village, Worker's Village, Hunting Party
For the Copper-player: Beggar to gain Coppers, Coppersmith to make them valuable, and Counting House to scoop them all up.
For the Silver-player: Trader, Feodum and Embassy all generate Silver, and Feodum rewards you for having it.
For the Gold-player: Tunnel speaks for itself.
The other cards all serve all three: Embassy creates the necessary draw, and the discard for Tunnel. Border Village provides the Actions, and can handily pick up components of each engine. Worker's Village gives the oh-so-needed +Buy. And Hunting Party can discard Tunnels and Coppers, and find that Counting House.
Other possibilities: Market Square (also gives +Buy, adds to the Gold player), Cache (for the Copper player), Gardens (mainly for the Copper player), Squire (for the Silver player and the +Buy and +Action). Jack of all Trades also generates Silver, but would dominate too much.