Transaction id wraparound questions

It seems that we have not been vacuuming our production database
properly.  We have been explicitly vacuuming all tables individually but
have not vacuumed the entire database.

A recent vacuum of the entire database gave us the dreaded
"You may have already suffered transaction-wraparound data loss."
warning.

We have so far encountered no problems but I am wondering about the
safest course of action right now.  We cannot easily take an outage to
perform a full dump and restore.

Questions:
1) What is likely to happen if we encounter transaction id wraparound?
2) Will a full database vacuum fix the problem?
3) Can it make things worse?
4) Other than dump and restore, what options do we have?

Information:
This query:
select datname, datvacuumxid, datfrozenxid from pg_database;

returns this:
"Production",1173213507,2246955329
"template1",  938856359, 938856359
"template0",        427,       427

All responses welcomed.
__
Marc Munro