Ah... but what you (and possibly Yamato) is missing is that they've sold buttloads of 1/48 valkyries and even more buttloads of 1/60 valkyries... so there are potentially several buttloads worth of customers out there. So that one (or two if they made 1/60 and 1/48) mold could potentially sell better than any single mold has done thus far, except the VF-1 mold. And with the far less moving parts involved (ie - no transformation) the mold shouldn't be nearly as complex to pull off.
Any Yamato valk owner would most likely buy one. Many would buy more than one. That's good math for a toy accessory.
Which brings me to my point about why GBP armor is cool. Aside from all of PC Valkyrie's original points, is that the GBP brings an additional amount of fun and play to the VF-1 toy. Just like the FAST packs do. Sure, I've got a 1/60 VF-1D, but my favorite thing is to have it steal the FAST packs from the 1J so I can "upgrade" to a more badass VF-1D. And with GBP armor, there's an awful lot of "badass". It just makes the toys more fun, regardless of how long it spent in the show, or how useless Hikaru was in using it.
It looks cool and any VF-1 valk can wear it. It's the perfect accessory toy. Personally, I'd buy at least a few if Yamato were to start making them. And as fan-oriented as they are, I believe it's only a matter of time before we see them come along.