From my experience, you only need 1x Escher. It's difficult to find a good time to use it, and often you sneak it in late game to completely pull the run out from under the corp. If you replaced 1x Escher with 1x Same Old thing, then even if you drew and discard the Escher early (or lost it along the way from taking damage), you would still be able to use it from the heap. Also, same old thing would give you the flexibility to use any of your other events for a second time instead. Just Imagine,You're low on credits, but your Yog.O.Saurus is tearing apart the corp, and you pull out a 4th tinkering to access 3 cards from R&D for the win!
Also, with Professional Contacts and 3x Diesel, you'll see even just that lone copy of Escher often enough.
From my experience, you only need 1x Escher. It's difficult to find a good time to use it, and often you sneak it in late game to completely pull the run out from under the corp. If you replaced 1x Escher with 1x Same Old thing, then even if you drew and discard the Escher early (or lost it along the way from taking damage), you would still be able to use it from the heap. Also, same old thing would give you the flexibility to use any of your other events for a second time instead. Just Imagine,You're low on credits, but your Yog.O.Saurus is tearing apart the corp, and you pull out a 4th tinkering to access 3 cards from R&D for the win!
Also, with Professional Contacts and 3x Diesel, you'll see even just that lone copy of Escher often enough.