Having held the Canon 50 1.8, and actually having seen one disassembled, I'd say pretty much everything has a better build quality than the 1.8. That said, build quality is relative, so it should be fine for everyday shooting, but for parties I'd like something sturdier.
Going from 1.8 to 1.4 isn't a huge difference, but it's quite useful in dim conditions. The larger the aperture, the better, and 1.4 IS larger than 1.8.
Still, for indoor (group) portraits, a 35mm would be a better choice, you will have to stand back quite a bit with the 50, and risk having people stand between you and your subject.