A lot of group psychology plays a role here. However, the ultimate principles of supply and demand are going to determine the value of cryptocurrency (bitcoin and others). I predict that the coins that are based on scarcity models will increase in value and the ones which have inflationary models will lag behind
Personally I think that Steem's inflation is one of the best things about it. In theory users should want to stake more coins because of all the inflation being generated by them.
In practice I believe that our inflation is making the currency more volatile in both directions. This is great for swing trading (x100 gains) but terrible for a stable asset that the community can count on. I think it will be very important going forward to create a consortium of whales who attempt to buy low and sell high to keep our value at a more even keel.