One idea to handle "dipping" into skills (only taking a couple of ranks) would be to "split" a skill.
Instead of choosing one class skill to get the class skill bonus (level +3), you choose two class skills, but you'll only get the cross-class bonus for each ((level+3)/2).
Allows spreading your stuff around without mastering everything, and it's quite easy, too.
If you want the advanced version, you could say you can dip in any two skills with one point and get half the normal bonus in each (-> class (level+3)/2, cross-class (level+3)/4).