There's not really all that much difference in the performance/fuel economy between a 71 and a 72 (I've put many miles on both, and got 22 city, 30 highway, pretty consistently, both with M41) and what difference there is is due to higher compression, better porting etc. on the earlier engine.

If your 70 ECU is working correctly, there is no reason to change it to a 72, which is not a straightforward swap. While both units perform the same functions, and use all the same components EXCEPT the cold start valve (which is 5V on 70-71 and 12V on 72-73) the main wiring connector on the ECU is laid out very differently. You could either figure out what each wire does and move them to the correct locations in the connector block, and wire up the thermo-time switch from scratch or, if you can find one, change the whole injection harness to the later type.