Interesting. I never heard of VAM until recently when Emma Pooley set an unofficial record for ascent speed in a GCN video challenge. I had to look it up to see what they were talking about, and this old thread on bike forums came up on the Google hits.
I don't use a power meter, Strava guesstimates are iffy and not particularly useful or accurate when trying to account for head/tail wind effects. And I knew I was a weak climber so I wasn't sure I even wanted to know anything about my VAM.
But the Elevate browser extension adds some interesting info from our Strava logs, so what the heck.
Turns out my VAM has improved from around 540 this time last year to 690 now. Still not a strong climber, but I'm pleased to see some progress. I don't feel like I'm any faster on climbs, but apparently over distance I am. I'm just paying too much attention to micro-data, how I do on those short, steep climbs of a couple hundred yards or half a mile around here. We don't have any long sustained climbs. But since resuming cycling in 2015 I've improved from dead last on every climb to middle of the pack on most and managed a few top tens that were heavily tailwind assisted.
Now I'd like to see Strava adopt some way to reliably factor in head/tail wind effects. There is a site that can analyze our Strava logs to estimate wind handicaps, but it doesn't seem to be maintained or updated now.