Paint is more than just "stripes-and-stickers", and the fact that the '06 Heritage is a real Ford-made variant, and people love them, for the look, the rarity, the historical connection, etc makes me think the premium is likely to sustain. There's just no other car that looks like it that's relatively obtainable.
Look back further, to say the mid 70s, when a real Ford GT was ~10 years old. How many back then thought they'd still be relevant, desirable and appreciating in value 40+ years later. Most would probably have predicted we'd all be driving electric cars or even hover crafts / air vehicles of some kind by now.
All that said, I'm not good at market predictions.