Josep beat me to the idea. >.<
While reading through my thought was to add failures based on shield strength and keep the "shield power" idea by simply having a Shield Reserve (SR) which gets marked off. In an example like OP's 3 soak/10 SS shield, the shield turns off after the 4th shot, so simply giving it Shield 3/SR 4 would be equivelent for what I was cooking up. Whenever you take a hit, reduce damage by 3 and mark off a SR box (on a ficticious gear stat card). This is where my idea ends for static (read: personal scale) types of shields.
In a dynamic setting like OP's ship shields, then there are two ways to play it. You can keep using a fixed 1 shield hit = 1 SR marked, regardless of the Shield value of any given arc (with the logic being the shield still took a hit and is drained regardless of how much shield is in the arc). For example, say you assigned Shield 1 to an arc. You get hit so 1 less damage is taken and 1 SR would get marked. If you had instead assigned Shield 4 to the arc and got hit then 4 less damage would be taken and 1 SR marked. With this take it falls on the operator to make smart placement decisions which optimize the shielded amount to Shield Reseve marked ratio.
A different and more forgiving take is similar to OP's rules earlier in the thread. The operator assigns Shield X to the arcs, then takes hits. One Shield Reserve (from a larger pool than the above) is marked for each damage shielded. Since players need to keep track of how much gets absorbed (as opposed to just "did I get hit?") for marking off SR this is a little more bookeeping than the first take.
Related topic: When I read through it seemed like they sent two different messages for ship defenses. The text for defense on p. 226 reads, "Defense reflects a ship or vehicle's ability to completely deflect or reduce the damage of incoming attacks or collisions though use of deflector shields, point defense systems, raw speed, or other, more esoteric, technologies." From what I understand, a TIE fighter is supposed to rely on its slim profile and speed to avoid hits, yet the TIE does not have defense. The stat blocks seem to imply Defense = shields, when the text state it's not limited to shields.
Incorporating rules like the ones in this thread shift shields to having more consistency (good), but also allow for more variable defensive concepts (tie speed and profile, point defense weapons, those weird gravity warping 'vong things) to be reflected in setback dice.