Ingenuity with 3-Star crafts

I did some basic testing and here are the results:

Careful synth
Base: 58
Ingenuity 1: 63 (+8.6%)
Ingenuity 2: 73 (+25.9%)

Basic touch
Base: 127
Ingenuity: 135 (+6.3%)
Ingenuity 2: 144 (+13.4%)

It does very little, when compared with the stratospheric gains those skills give you on 1 and 2 stars. Ing 1 is almost worthless, but 2 is decent.

For progress, I normally use SH2 with Rapid Synth 3 times plus 2 careful synths, with no ingenuity. ING2 gives enough of a boost to cut one rapid synth. Hardly a deal for 32 CP, plus the opportunity cost of potentially giving up some tricks of the trade and the added requirement that my final synth have Ing 2 on it (another 32 CP).

Comparing Piece By Piece to Rapid... Your first one does 133, second does 93. Rapid does 120 for 0cp but at 80% success compared to 15cp and 100% for PbP. Also, the typical rotations for PbP require Ing 2 at the end for your final 3 CS. One of the central arguments for PbP being superior was CP saved by not using Ing 2 because 1 and 2 stars taught us Ing was essential, which I have found is not the case for 3-stars. Note that for furniture or 3-star elemental crafts, PbP is still better.

As for the quality piece, I have found Ingenuity and Innovation to be more useful as ways to fish for Good conditions for Byregot's if I have enough CP. The +50% is better than both of those buffs put together. To finish, I will use Steady Hands, Great Strides, and then use Inn and Ing unless a good condition pops.

I have also found that if I haven't built enough IQ stacks, I am better off investing CP into more touches than into Ing and Inn. I don't have hard numbers for this and am feeling too lazy to construct an example.