I'd start with my 2004 550SE. Ditch the ugly trapezoidal exhaust tips (already done) and change out to lighter, better-sounding exhaust. (check.) Next would be building the 3.2 to 3.6 specs to bump the torque. I'd lower slightly (no massive drop that compromises real-world usefulness.) While I love the stock 2002 Carrera Lightweights with Seal Gray painted wheel centers, I'd like a little variety now, so would replace with HRE 560c.

Nothing too radical.