The only problem with switching from synthetic to dino and back is oil leaks...I am a once you start never stop when it comes to synthetics...
The reason is actually pretty simple...The molecular structure of synthetic oils is actually smaller than that of conventional dinosaur piss.
That being said, the synthetic tens to cause some very minor oil leaks when the switch is first made, normally goes away in a month or two....
The other issue is some synthetics simply wont mix with conventional oils (mostly paraffin based oil)...
I would definitely agree on the running of a better filter, but I am a firm believer in synthetics (some of our dyno runs have proved it to be worth some HP too)..The biggest difference for us was oil return control and temperature control...
This subject can be debated forever however.....

GT