I used to be the best sprinter in our group of maybe 30 frequent group riders, all of them younger. I did what I did to get better at it. I couldn't say if the following would work for anyone, but it did for me and did help my endurance riding for whatever reason. I'd start this once-a-week sprint training a couple months before my A endurance ride of the year.
The only sprint training I did was hill sprints OOS and did them near the end of a 20-30 mile week-day endurance ride. I wouldn't be particularly tired then, just well warmed up and riding well. I did one set of 6 X 45" X 5' sprints up 6%-8% hills. I focused on pulling up hard enough to almost lift the rear wheel off the ground, hands in the drops, but not deep. butt back with legs just brushing the saddle, pulling up hard on the bars, hard enough that if I didn't pull up on the pedals hard enough, I'd lift the front wheel off the ground. Cadence wasn't terribly high, maybe 80.
My impression was that this was good for leg fiber recruitment and increased my leg speed OOS in a flat sprint. It seemed good to be able to push and pull with all the muscular strength I had at a continuous power level and cadence for that long. Because of the focus on strength and technique, it seemed to help my endurance in hilly terrain. Even though we don't pull up in normal riding, still the back leg has to get out of the way. We certainly don't want to be lifting it with the front leg. I think the story above in post 8 about riding fixed speaks to this.
I don't have any numbers from those days, no PM. However I now (77 y.o) have a 5" 684w and average 467w on a 32" hill and I'm 4 seconds slower than I used to be in my 60s. Nothing great, but good enough for most purposes. I'm 2" away from matching the AG KOM on that hill. I was lifting in a gym fairly regularly then but haven't been doing much of that lately, nor have I been doing any real sprint training this year: I don't recover quickly from max efforts now. I think they'd cut into my endurance training too much. That wasn't an issue in my 60s.
All that said, I doubt that anyone could reasonably estimate how much you might be able to improve. Everyone's different. And that said, what difference does it make? I'm sure you could get better at it, and why would anyone not want to get better, there being IME, no downside?
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