nothign. unles syour current ignition isnt up to par, or your running forced induction adn the spark is getting blown out. but thats not "gaining" power, its getting it back. ignition systems dont gain you anything. they simply get back lost power
sure. if your ignition is workign porperly, i see no reason to buy a box, unless you need the rev limiter, or somethign else that they offer. i knwo the digital6 from MSD has a nice 2 stage limiter, and they all have soem very good features. if thats why your loking into an ignition box, then mreo pwoer to you, but dont waste $$$ on a box unless you need the features or extra spark
i spent about $1000 on new ignition equipment from MSD and I must say I did see a difference. Not that it was anywhere near the feeling of $1000 worth of engine mods, but the car idled way smoother, and I could gap my plugs to .060 and pull HARD up to 6k without any blowout whatsoever. Which before, my car started to lose power at around 5k with the stock stuff. I got the 6AL box, the heli core wires, the MSD coil, and the billet distributor.
if you have the cash, buy the msd stuff. I put the msd, 6al, billet dist, blaster coil,and firewire plug wires(which are awesome) and noticed a world of a differnce, the msd does not drop off spark in the upper rpms where the stock ignition cant keep up, adding more top end power and cleaner running lower speeds with smooth accell.. do it and be done, no drawbacks.