Come to think of it, when we refer to reinforced Yamataiaum, we are talking about a yamataiaum hull covered with xiulurium-coated zesuaium plates, right? That's the way it is with the Sakura-class gunships, I believe.
So, the improved plating would incidentally be part of the stealth plating too. I shall adjust the proposal to reflect that.
This would allow the Himiko-class to have two easily obtainable add-ons (the improved shielding and the better stealth/zesuaium plating) in contested sectors while other Himiko models serving elsewhere could be the less costly basic version, which would be upgradable should the need rise (there's a difference between patrols and freighter escort vs. war against the Mishhu).
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Of mention - in case it wasn't noticed - the Himiko-class has propulsion systems which are vastly below part of current KFY standards. Zakalwe suggested the STL speed might be a bit low for when the ship would need to use its CFS to do other tasks like concentrate on shielding, projected energy beams or deploying interdiction fields... but otherwise while I might agree that raising FTL speeds to .75~.80c might be a good idea, I don't think the CFS FTL and foldspeed need to be higher.
CFS-based FTL speeds are mostly used within solar systems. At 15 000c, you can cross over the solar system from the sun and reach the most distant solar system body (Sedna, 90 AU away from the sun) in 3 seconds. This proves it is quite sufficient for the use it is put to. Seeing that CFS devices are one of the mos costly element on Star Army vessels, economy there in favor of hyperspace fold drives seems a wise thing to do.
In circumstances when an hyperspace fold drive is not useable, such as in a nebulous environment... the top speeds reached by KFY starships so far are around 11 700c - so, the ship merely travels at 2/3 of it's usual speed, instead of being reduced to 1/30th like the Sakura gunships.
Alternatively, if the fold drive are just plain damaged, 15 000c is sufficient to cross over 1.7 light years in an hour; or 41 light years in a day... which is enough to cross from the center of the Empire to one of its outer boundaries. This looks reasonable.
As for the reduced power of the fold system, 0.43 light years/minute is actually 15 times faster than the CFS FTL speed. It allows to cover 40 light years in the span of around 81 minutes (1 hours 21 minutes). Is this slower than most modern KFY vessels? Yes.
Are faster speeds actually necessary? For rapid response vessels like the Sakura-gunships; perhaps. But for ships whom merely patrol from within specific boundaries, hold garrisons at worlds or just explore out of our territorial boundaries with the intent of exploring (especially in nebulas), this is hardly an impediment. If greater speeds are needed, nothing stops a Himiko escort from going piggyback with a larger Irim, Ayame or Chiharu warship to reach its destination faster if speed is truly necessary for a deployment - after all, they are meant to be escort vessels when operating within a squadron or fleet.
The huge advantage with trying to be economical with the engine output is the reduce power usage, which can go to weaponry and defenses (unlike the Miharu, which had a considerable handicap there) and also holds the non negligible advantage of being a good-quality, inexpensive ship models to produce. For the resources needed to build a Sakura gunship, nearly 3 Himikos could be built - each being nearly as effective as the Sakura light gunship in term of combat performance.
If this philosophy can be successfully applied, it could put in question the whole building scheme of currently used Star Army vessels (for example, one could maintain that it would be more economical to limit the Sakura to a 20 000c capable-CFS and a 0.59 ly/m fold system - the light gunship might not actually need more), but the resources and power saved by such approaches would be sizeable.