There probably would be a noticable improvement in life. To be honest untill the CTC-2 (I ranout shortly before that) I had been using mostly fuses from electronics I had been scrapping and hadn't checked if what I had was slow blow or not.
BTW: line voltage affects these a good bit. There are usually 2 line voltage taps on the transformer primary on most RCAs having it on the best tap for your line voltage or even runing the set off a variac set for balance between normal picture and minimum H output cathode current is not a bad thing to do.
Couple of other things you can do are to make a ventilation hole in the HV cage and mount a small fan to draw warm air out to cool the flyback. Also on the CTC-16 I serviced for a dead beat (guy still owes me money) that used to be active here. He wanted me to remove the rubber tire on the HV winding and replace it with Silicone based on this video:
https://www.youtube.com/watch?v=BUnPkymnxUw which I sucessfully did for him. Apparently the rubber beraks down and becomes conductive sometimes as it ages.