If you put the parts in a protected place, the minimum as specified on the materials info pages is sufficient, especially if you use WSF.
For more exposed parts, especially in "Detail" materials, I would use something like 50% over the minimum thickness. Also check out the detailed materials descriptions, they have some advice on thin parts.
Also, if the part is large, smoothen a bit the point where sprue and part join, otherwise it tends to break easily in such a spot. I see a risk like that in the plate at the bottom of your first picture. Maybe also use two sprue links rather than one there.
Greetings
Karl Heinz
Last edited: Aug 16, 2012