Think of it this way: if you own 100,000 bitcoins and you know there won't ever be more than 21 million bitcoins, then you currently own 0.47% of the whole "bitcoin pie". Now if the upper limit changes to 210 million (thus the pie getting bigger), then your share of the pie suddenly shrinks to 0.047%.
If 21 million cap is multiplied by 10, then all savings are multiplied by 10 as well. So 100,000 bitcoins will become 1,000,000. It's still 0.47%.
I disagree. As I understand this, the cap is the sum of a (geometric) series, adding up all the bitcoins generated per block over time.
So you can't change the upper limit directly, but you could change the number of bitcoins generated per block and / or the reduction rate (which currently is at a 50% reduction every 4 years).
When changing one of these two, the projected upper limit changes, but the number of bitcoins in my savings stay the same. I don't see any reason why the number of my bitcoins should be affected by this.