I think the best solution for allowing simple logic gates to be made would be to change the way wires work.
Instead of propogating a pulse, wires would store an on or off state. Then a not gate item would be all that is required to make logic circuits of any complexity (one not gate feeding into another to make a diode, two diodes feeding into one not gate to make a nor gate, then combinations of nor gates to make any logic circuit
https://en.wikipedia.org/wiki/Logic_gate#Universal_logic_gates). Of course having other gates as items would greatly simplify things.
A not gate would even be usefull as a colour changer for wires. If you want two red wires to cross but not affect each other, use a not gate to change one of them to another colour, cross the other red wire, and then another not gate to change it back to red.
Both Minecraft and Starbound have wires that store state, not gates, and wires that can cross over each other. These three things allow for the creation of immense logic circuits. The best method in Terraria currently is the use of the hoik glitch, which is rather more limited.