after level 38 when ALG's bottom out is when you start taking less of a hit for investing in SA's... but I have started on some dots at 48 and low 50's.. most I am waiting until low 60's.
I don't add sp's to the SA tree until after level 60. I think that it is more important to get the build right than it is to add to the SA tree early on in the dot's build.