160 million is a very low number. I manage production databases which reach this value in a day easily. As other said, 200 million is the default threshold for the anti-wraparound vacuums. I wouldn't worry, specially for template0.
That said, there is nothing preventing you from temporarily changing DATALLOWCONN, running vaccuum (which should be very quick) and then changing it back. But you should not have to. I do that in our production database, but only because it suffers from a bad schema design and we ended up with thousands of tables, which is too much for the autovacuum workers to cope alone, so they need a manual "boost". I still don't disable autovacuum.
I don't really understand the bit about autovacuum changing query performance. In which scenario would it be preferable to have outdated analyzer statistics? This would be like running a system with garbage collection disabled because GC can increase the amount of free memory. That's the whole point.
