Does increased rarity chance works on chests and similiar objects

There is a penalty for some levels delta, indeed:

There is a penalty to the chance of currency items (scrolls, orbs, etc.) dropping in areas with a monster level more than two levels lower than your character level. For each additional level that you have compared to the area's monster level+2, the chance of a currency item drop is reduced by 2.5%.

So if you are level 30 in a level 20 area, you will see 20% less currency item drops on average: 2.5*(30-(20+2))=20

A level 30 character in a level 28 area will see no penalty.

Source: http://en.pathofexilewiki.com/wiki/Drop_Rate

The way I understand it: there is a penalty for currency items only, therefore nothing for other items.

From the mechanics thread:

Increased Item Rarity Increased Item Rarity % modifiers increase the chances of an item being magic, rare, or unique. For example with a total of +100% increased item rarity, you'd get twice as many magic items, twice as many rares and twice as many uniques from normal enemies. This modifier has no effect on the number or type of currency items, scrolls, or gems that drop. When in a party, only the modifier from the player who lands the killing blow on an enemy is counted. If one of your minions gets a kill, the minion's IIR is added to yours and the total is used.

Magic, rare, and unique monsters have an Increased item rarity modifier for drops.