Hi,
I just installed an MSD DIS-4 on my car a week ago.I had the same questions as you and wondered if i should and/or needed it.
wel,i must say i am very happy with my decision to install one.i noticed a definete improvement in how my car ran.it idles better,it is more responsive and it seems stronger at higher rpms.i launch my car off the emergency brake so i hooked the low rpm rev limiter to the switch on my e-brake that triggers the brake light.
now i apply the ebrake,bring the rpms up till it hits the rev limiter and then when i pull the e-brake release the rev limiter turns off at the same time the car launches.it works better then i thought it would.
im my opinion it is a definite improvment.
thanks,nick