There is no difference.

However, in my opinion "вполне" is used more in contextes where doubts exist.
That is:
"У нас денег вполне достаточно, чтобы ..." looks more like phrase from discussion of reasonability of purchase.
"У нас денег полностью достаточно, чтобы ..." looks more like statement.

But I cannot say is it common practice or just my point of view.