Currently, I am simulating an audio amplifier connected to a loudspeaker with long wires.

Qucs already has some nice components to simulate two wires:
"4-Terminal Transmission Line" with parameters Z, L, Alpha & Temp
"RLCG Transmission Line" with parameters R, L, C, G, Length & Temp
"Twisted-Pair" with parameters d, D, L, T, er, mur, rho, tand & Temp

What I would like to see is a component similar to "4-Terminal Transmission Line" i.e. two parallel wires = 4 connections, but where I can specify their surface (A), distance (D), length (L), conductivity (rho), frequency (f), relative permeability of the material between the wires (mur), relative permittivity of the material between the wires (er)
Qucs should then calculate the wire radius (r=sqrt(A/pi)) and subsequently R, L, C & G (for example using www.mathworks.com/access/helpdesk/help/toolbox/rfblks/twowiretransmissionline.html)
rho, mur & er should be dropdown lists (combobox) where you can choose frequently used materials (copper, silver, aluminium, air, PVC). This provides a user-friendly method to model two wires.

BTW Qucs is great!