The success of Trouble has me questioning almost everything with Ayu. I don't understand how it's still selling. Through my perspective Trouble is Ayu's weakest release and least promoted release but yet here it is selling 30,000+. Months after release. So I have no idea if A Best 3 would sell well or not.
My guess now is that it would sell less than A Best 2 but would still sell more than a regular album.
As for remastering? I don't think it would matter unfortunately. I would love it if they fixed the dynamic range of the tracks. But in 2018 the music business still refuses to change their practices aka "the loudness war".