SA alone is not useful with average players. If we really have to put an exact value with SA, it could be somewhat close to 1 additional * onto that particular attribute where the effect is triggered in a set circumstance. Therefore, our team should also have been set up in some particular ways to ‘force’ the engine calculation to trigger the SA abilities more frequently.

Will illustrate a few possibilities with my team, players and stats for your reference below.

Team setup: 4-1-3-1AML-1. Left flanks players pulled back plus ST moved slightly left to create a 4-player-flank overloading effect when facing superior opponents.

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Team is as good as its players, which comes with our own build with power training. Level-3 freeloading club here, so resource-wise my team isn’t better than the rest (and definitely poorer than paying managers).

20yo ST. Joined at first season. Somewhat between 1st & 2nd class FT via auction- as constrained by limited budget in season 1
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Build: ST is built to play as lone ST/AMC to burst through defence with speed and finish 1-on-1 chances with build-up play via defensive and counter attacks, hence high finishing & speed. High creativity as usual to increase chances of SA being triggered. Decent headed & positioning in help scoring CKs.
SA compliment: 1-on-1 scorer SA - theoretically finishing should be 260% with SA triggered; 2nd SA is an undesired special sponsor reward (would have preferred shadow striker, though better than CK taker)

19yo AML/C/R. Joined last season. 1st-class FT via auction
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Build: With similar strengths of ST, this AM is specialised more in also dribbling and shooting as a winger. Most fullbacks could not contain such a speedy dribbler with high shooting ability. High heading is a ‘by-product’ with white averages training which the player benefits from scoring lots of CK goals
SA compliment: Shadow striker SA for wingers is close to a default for teams whose main scorer is the AML/R. 200% shooting should come with no reduction in penalty with SA triggered (shooting stat ‘could’ be reduced with long shots, and SA should mean it stays at 200% and not lowered)
Also is FK taker with both high shooting and finishing (would change to ST for FKs once AM misses 2 FKs)

18yo AML/ML. Joined this season. Bought as recommended player as close to 1st class FT - FT budget spent on DC, hence money left could only buy base-price player
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Build: Just 18 days since joining, so his stats are not as good as the other 2 seasoned players. Main focus is on passing & crossing, plus the usual creativity. He would be played as ML to compliment left-flank counter attack when facing superior opponents, or AML against inferior opponents with AM shifted to the other flank
Trials: Purposefully let him take all CK duties, despite lower crossing than AM. Average 2 CK assists every 3 matches, which is a decent return. AM benefits from more goals scored with high heading. DC/DMCs also surprisingly scored a few more CKs than usual.
SA compliment: Would add CK SA at start of next season with pressing drill (greys dropped with lowest average). Should boost CK crossing to 180%+ when SA is triggered

The above works for my team and its setup. And as we all know, each of us has our own preferred formations and orders which could work perfectly too. With SAs, we could look into how our team scores the most and add them on accordingly.