So are birthday minis valueless now?

Pretty much.

The only ones with any value are the ex asian minis in 7th boxes.

The more normal purp, gold, green are flooded from (almost) everyone getting 7th boxes from vouchers on older characters.

I'd almost argue the white minis are sometimes harder/more annoying to find ones you need if you are trying to fill you HoM nowadays... but still not worth much