How it currently works:

Currently Lerasium and Lerasatium increase your metal strengths to 16, and then +1 afterwards.

Canon

In canon, the size of the Lerasium dictates how much stronger you get. If Vin were to eat the lerasium instead of Elend, she would have been far stronger than a lerasium-mistborn Elend.

There's also the idea of lerasium alloys, which allows you to take a piece of lerasium and alloy it with other metals to make mistings of those metals. It doesn't have to be optimal, but you could theoretically funnel all that power of lerasium into a single metal, granting insane strength in one metal rather than great strength in all of them.

Changes Proposed:

• The god metal nuggets need to come in different 'sizes'
• Consuming a nugget gives proportional strength based on the size of the metal, rather than setting your strengths to 16. This would make it so that your starting metal would be far greater than your other newly gained powers.
• Alloys of the god metals can be made and used, allowing you to divide the god metals strength between what you're making. This means a tiny tiny piece that would grant 16 strength total could be divided and alloyed to give you 10 extra strength in steel and 6 extra strength in tin.

This does mean that power strengths would need to be rebalanced to make more sense. If Vin was an 9 strength mistborn, the lord ruler would probably be a 12 strength. A very noticeable increase. This also feed into spike strengths, where inquisitors would have two of the same spike to be slightly stronger than your average metal born, though maybe not stronger than a lerasium metalborn.