Replace vs Re-power

Is there any benefit to replacing an engine instead of rebuilding?

Cost

Years of service

Gas vs Diesel?

Reliability (they don't make stuff like they used to)

Would it be better to re-power a 12 hp Gravely Commercial, over 15 years old, that is used mainly for ploughing and tilling a clay loam soil?

How much bigger?

What is the limit for size with out having to alter the frame or using adapters?

Thanks
John

What engine do you have?

Kohler 12 hp, other than that I don't know. The tag that has any other information is unreadable.