Upgrading to the v1.4 electronics can provide significant benefit to your v1.2 device, and a modest benefit when upgrading from v1.3 FarmBot. Perhaps the most notable benefit is that the v1.4 Farmduino electronics board features an STM32 co-processor that allows the board to keep much better track of the rotary encoder signals than was possible with just the Atmega 2560 chip featured in the v1.2 and v1.3 electronics boards. This allows the FarmBot to move more reliably, accurately, and at higher speeds than before.

Furthermore, the v1.4 electronics feature a streamlined single power cable (better than both v1.2 and v1.3), an easier-to-use and better-sealed electronics box (since v1.2), easier-to-use unified connectors (since v1.2), an IP67 rated waterproof power supply (better than v1.2), and the system runs on 24 volts rather than 12 volts (better than both v1.2 and v1.3).
Applies to v1.2 and v1.3 kits
Benefit Medium to High
Cost High
Difficulty High

The upgrade requires the following parts:

Qty Part
1 v1.4 Farmduino
1 v1.4 Power Supply with modular power cable
1 v1.4 Electronics Box
1 Farmduino Data Cable
1 Raspberry Pi Power Cable
1 USB Adapter Cable
1 24v Solenoid Valve
1 24v Vacuum Pump
1 Solenoid Valve Cable and Vacuum Pump Cable (required unless you add the new connectors [compatible with Molex 151048-1206] to your old cables)
1 v1.3 UTM Cable (if keeping v1.2 or v1.3 UTM)
v1.4 UTM Cable (if also upgrading to the v1.4 UTM)
1 Set of v1.3/v1.4 Motor Cables (optional, but the unified connectors are very convenient to work with!)
1 Set of v1.3/v1.4 Encoder Cables (optional, but the unified connectors are very convenient to work with!)