Until lvl30 i only trained a little lightning for the imbues to be able to actually do some damage
As i see it, doesnt matter what skills u choose, if ure gonna max lightning and fire trees, just buy everything or what u want, as long as u got SP enough to pay for it.
At lvl30 you should have Lightning nuke, Fire nuke, Must Piercing Force to be effective tho, so save some SP for them =j
(i kept my highest skill mastery about 3 levels below and i could afford it all.)
Just max out everything, except for what you really dont think you will need (increased physical damage buffs etc

).
An int nuker maxing spear ? Im a but unsure about that, you wont be able to drop off any huge physical damage anyway, if you are going for INT, i'd say no spear (except maybe lvl10 or 20 for extra HP, the last skill in spear series). Might be wrong, if i am, im sure someone like Suicidegirl will be here to correct me in a moment =)