Yes, powerful countries should intervene in weaker states' affairs when needed. When a nation amasses power, that nation also amasses considerable responsibility, and should use that power for the good of all, even if it means interfering in the goings-on and affairs of smaller, weaker nations for the good of those nations.
Powerful countries should not intervene in every single weaker state affair. However, in certain drastic circumstances it is absolutely necessary for the powerful countries to step in and help others out in these affairs when in need. If these powerful countries never intervened, then some states could have possibly become extinct due to massive conflict with others.