You do not gain any power with an alky kit, but it does allow you to turn up the boost for more power IF the other components supporting parts are capable and matched to the HP level you want to achieve.
Your 25 year-old car does not have the fuel supply and engine management capabilities of new cars that are better built to handle an increase in power.
For example, a stock GN fuel pump was barely adequate when new, and normal replacements are not much better.
Short answer is there is no short answer. Power gains vary. It all depends on your combo and your tuning. A car built and tuned running 116 may not gain much while a car with the supporting mods but on street gas may end up near the same power levels as race gas. Difference is instead of burning the expensive 116 while sitting at the stop light and putt-putting around or having to dial your tune back to run 93 when you're not at the track is with alky you can leave the car set on kill all the time and it only kicks in when you need it. If it is a track only car then the benefit of alky is questionable but if it is a street car then imo one of the best bang for the bucks you can get.
Basically what will happen if you are able to tune the car properly is you will have the ability to reduce your e.t. by about 1 second over a 93 tune. A car that runs 12.0 on 93 @17psi/17-18* advance "could" with the proper "stuff" and tune run 11.0@26-27psi with enough supporting stuff and tuned. IMO it's more fun when the car is close to stock and you have a good handle on the tune with no detonation then you go with razors alky and dial it in with that. You will probably never do another single modification that will give you the more potential power gain without doing extreme engine modification that will allow the engine to be operated at higher rpm and with better mass efficiency.