The engines on a modern airliner spool up pretty quickly, but remember, there's a lot of mass to move. I've been in a full motion 737-500 sim at United's training center and remember doing go-arounds, I don't remember any great delay in engine response time or large time lags to get the aircraft airborne again. Now in comparison, when I flew the L29 you could be looking at a 20/ 30 second lag from going to idle to full power and you didn't dare slam the power levers forward (you could induce a flame out). In an aircraft like that you always made sure you had enough airspeed so if you did have to go around you had time for the engine to spool up. Personally I liked to turn base to final a little fast and a little high because of this and could make final corrections with the speed brake.