But the chain shirt can also be combined with the buckler, as well as the usual dastana and chahar-aina, and at that point, while relatively expensive, it's a decent boost to AC.
No, it's not a decent boost to AC. First off, lets be clear that we're talking about a Sor/Wiz that's around level 6 or 7 buying this stuff, because before that point he's just not going to be able to afford to blow 4k gold on this junk. Why not? First, it does squat for his touch AC, which a much more important number to a Wizard. Second, even if we're talking about a Fighter getting a +7 bonus to AC, that sort of boost is starting to lose it's usefulness at this point.
Thistledown Suit + Githcraft Buckler = -0 ACP, 0% ACF, and everything needed to start picking up armor mods which might actually be useful like Mindarmor and a Lesser Deflection Crystal. With the money you save, you can grab a lesser extend rod, too.