VAM may not be relevant to our area since our longest "climbs" are maybe 2 miles long at most, averaging only 1%-2% with undulating brief peaks near low double digits. But the Elevate extension for Strava adds some info that helps confirm I'm making some progress.
I try not to obsess over the data or think about it during a ride, so I don't bias my rides with extra effort to "prove" I'm getting stronger when I'm actually just redlining at an effort I couldn't sustain for more than a minute. But after some recent bike tweaks -- sealed bearing pulleys to replace the draggy old sintered bushing bearing pulleys; raising the seat post/saddle a bit to encourage myself to spin rather than mash -- Elevate's data, including VAM, shows some improvement -- from 690 to 720.
But I'd need to find some real sustained climbs that last longer than a couplafew minutes. Best I can do locally is repeats. The brief eased effort between climbs is like interval training, which doesn't really test how I'd do on a sustained climb. I already know I can recovery fairly well with 30-60 seconds of recovery between efforts.