How amateur??? I am not the best player even my house has ever seen. That being said I have placed and won my fair share of tournaments. To be honest, I didn't even know "playing the Ghost" was a thing until I visited this forum.
If you can keep your wits about you and make an average of 4-6 balls every time you step to the table, you can win just about any tournament that doesn't involve upper tier players (and maybe some that do).
Walking in cold with no tournaments in a while...it will depend on how quickly you can work out your jitters. A lot of the time not knowing who the opponent is, or their reputation can help. No fear means a clear head.
I remember walking into my first 9 ball tournament here in Texas a few years ago, drew a guy named TJ Davis, honestly I didn't know the guy from Adam, I beat him 3-1, but I guess he is some notable player from the area. My next opponent was Jeremy Jones (super nice guy and all around good sport and fantastic player), and being new to the area I just thought he was some dude named Jay (couldn't really hear his name when they called it), turns out he shot pretty sporty, but I took him to hill hill in a race to 3, where he proceeded to get out rather quickly and my night was over with a 3rd place finish (out of 27). All that and I am only a 6 in TAP league 9 ball.
All that to say, if you don't get in your own head, or let others do so, if you are capable of running a rack...anything can happen in a tournament. My suggestion, show up some place and test out your theory, but get there just before the gun goes off and don't worry about anyone but you.