With as rare as they are, they should be even more worth it with a stat boost, even if it's something little, like an "All Stat Boost" of say, 5, or even 3. Or even just one stat. But maybe to hatched shinies only? I don't know.
PSN: Echidneys // 3DS: 4468 - 1242 - 8413 "It sucks, and you're all stupid for liking it."
How about if shinies were to have their natures effects boosted x2? So, not only does it double attack bonus, (lets assume adamant nature) but it also doubles the amount taken from special attack. The only issue I can see is that it makes Pokemon with non-mixed sets somewhat broken, but given how rare shinies are anyway. . .