Chance in a Dice/Pip Stat/Skill System

Just had some thoughts on the interesting dice mechanics in OpenD6 and how it avoids the additional math introduced in abstracting this to numbered skills and modifiers.

In the OpenD6 system, skills can be purchased down to the pips on the D6. This is a fascinating idea where they remove the numeric skill or modifier math and go right for the dice jugular.

I'm interested in the chance math behind this. The D6 system only allows +1 or +2 before the player moves to a full additional D6. Technically, moving from +2 to D6 induces the chance that a 1 comes back on the D6, which leads into the wild dice mechanic.

What really is the cost benefit of moving to a D6 vs. potentially rolling a 1? You'd immediately improve best case scenario by 4, which seems quite vast in a 2-3 dice pool, while running the risk of rolling a 1 or 2, which puts you at the +1 or +2 level or worse.

If it was broken down to purely just +1, +2, D6, is there a method to expand "pip-buying" beyond D6 and avoiding additional crunch/complexity such as the wild die?

Does anyone else know systems that allow for breaking down dice into pips or direct "dice purchase" during character creation?