Should time spent on system mechanics be based in interest or importance/risk?

[pemerton]

Can you resolve the which-system-to-use problem by letting either the GM or players declare which system they want? The players call for the heavyweight system if they're interested, and the GM calls for the heavyweight system if he thinks the stakes are high?

This is basically Burning Wheel, although it puts more emphasis on player than GM preference - I mean if the GM thinks the stakes are high, and the player disagrees, the player is probably correct, yeah?