In recent days there appears to be a number of posts on minimalist techniques when refereeing Old School sessions. Here and here are examples.
My view is that, is that we should enjoy the wealth of options we have today. Everything from elaborate Dwarven Forge setups with detailed miniatures, Dungeon layouts projected from overhead onto the table, to session run with nothing more than pen, paper, and dice.
I feel the key thing to remember if you use elaborate setups that you should be able to still be proficient with the basics. Because not every situation is going to call for pulling out the box of dwarven forge miniatures. I know for me my games returns to a more basic setup anytime the players start running around City-State or the countryside. All that on the table is a poster size color player map and a counter (penny, a miniature, etc) to track their location. Sometimes I don't have that and just use one of my 8.5 by 11 black and white player maps with the players making note on their player map.
Things like Dwarven Forge products appeal to our inner geek, but they are also a powerful tool for communicating what in our minds.
That is key.
A successful and fun session demands that the referee and players are able to communicate with each other what the hell is happening in everybody's mind. Without that the game becomes an exercise in frustration. Frankly one of the difference between 1974 and now is that we know more techniques on how to drag what in our heads out to show the players.
Finally not everybody is competent at the verbal only approach of pen, paper, and dice. We all have different strengths and weaknesses. Miniatures, Dwarven Forges, overhead maps projectors allows referees to do things that that they would otherwise would be bad at.
So keep your skills up at using just paper,pen, and dice. If you are using overhead projectors, dwarven forge, etc; I hope you and your players are enjoying the hell out of it.