A VDP is just a point for a pilot to go missed, like an MDA.
Not quite. If you look at the definition of the VDP, it is merely the point at which the normal glide angle to the runway (3.08 degrees in this case) intersects the MDA. The missed approach point is always farther along,
usually at the end of the runway, although it's actually 0.5 miles short of that on this approach (probably because the terrain beyond the runway would otherwise compromise the missed approach procedure or require a higher MDA). Executing a missed approach turn before the published MAP can compromise obstacle clearance or airspace, so while it's OK to climb if you don't see the runway by the VDP, don't turn until you reach the published MAP.
VDP's are not regulatory, they are the same altitude as the MDA.
While the VDP is reached at MDA, the MDA is a line along the final approach course while the VDP is only one a point along that line.
So at MDA you would either see the airport environment and descend (at the VDP) or level off at the MDA until XEXXA and go missed.
Most instructors teach instrument trainees to descend to the MDA expeditiously, resulting in reaching and leveling at the MDA before reaching the VDP. This gives you time to stabilize the aircraft at MDA, and look for and find the runway before you reach the VDP (published or self-computed). You would not want to descend below the MDA before the VDP, as this shallow approach could compromise obstruction clearance before reaching the runway. OTOH, once you pass the VDP without seeing the runway, you know that the chances of completing the landing "at a normal rate of descent using normal maneuvers" are decreasing rapidly, and a missed approach is increasingly likely even if you eventually see the runway before the MAP.
On this approach if you use the non local altimeter, you reach MDA above the VDP altitude.
You could look at it that way, or you could say you reach the true VDP for that MDA (as opposed to the published MDA) further from the runway.
But you would think the VDP would move up 100 feet too, right?
The MDA moves up 100 feet, but the VDP moves out by the distance required to descend 100 feet on (in this case) a 3.08 degree descent angle, which computes out to 1858 feet, or .3 miles. Thus, when using the alternate altimeter setting, you'd want to consider your VDP on this approach to be 1.0 rather than the published 0.7 miles from XEXXA.
Remember -- VDP is a point, not an altitude!