Some excellent questions!
Couple things to consider about longer or larger diameter flying lines:
1) Longer or larger diameter flying lines do increase drag. As a result a kite will sit deeper in the window.
2) A side effect of longer or larger diameter lines is the reduced AOA (de-powering) caused by the increased catenary (sagging) in the front power lines. This can create a problem at the edge of the window where there is less tension on the lines and even more catenary as a result. Some more efficient kites may try to tumble out at the edge as a result.
3) Longer lines are less responsive as you need more bar movement to remove the catenary in the rear lines before any steering input is made. This is also a problem at the edge of the window.
Leading edge and canopy wear:
1) Leading edge micro-wear will not have much of an effect on performance.
2) Canopy wear which normally presents as increased stretch and distortion can either make a kite more or less powerful depending on the kite design, panel orientation and reinforcing. If it results in increased shape (bagging out) the kite will sit back more and be more powerful but less efficient. If it results in a loss in profile shape, the kite will lose power and most likely (but not always) efficiency.
Generally speaking, an older substantially worn kite will not go upwind as well as when new.
increased drag due to micro-wear on the leading edge and canopy vs. it's brand new condition.