Well firstly can I just say this is an awesome thread, one of the best metal threads I've been through, Good discussion

Yeah I have been practising slap a bit lately, but I don't know why because I know it's stuffing up me maintaining good technique. But now that I am about to start up lessons again I think I will put it away.

Fact is best band with best bassists either don't slap or it is an occassional fill, but really their are cooler effects that can be created by other techniques or simply awesome sense of Rhythem (which is what the bass is for not slapping).
Leave slapping for someone like Whooten (is that right spelling, only just discovered him)

My view is 4 string all the way (not a fan of the 5 string)
play the bass properly