Yeah, directions have been a problem - aside from North and South (and those aren't entirely satisfying), We have "beside" but no way of saying which side when not in sight. "up, down, in front, behind, above, below" are all covered sorta (but "sorta"" is usually as good as it gets in a minimal language).
"Keep, save" is probably either 'awen jo' or the reverse or even just 'awen'.
"Planet" generally seems to be covered by 'mun'. 'sike', as you note, covers all things roundish in 2 and 3D (and this is not an obvious place to expand vocab.)
"machine" and tools in general are covered by 'ilo' (which, as a match with 'kepeken' could be eliminated -- or 'kepeken' could be).
Vehicles tend to be seen as constructions, 'tomo', with modifiers.
"Insert" or "puncture" or "poke" or "hit" (and these may be more than one), do seem like an area in need of some filling.
"cultivate" gets lost in general work, 'pali', though several extensions might make it clearer.
Most of what we have could be improved , I'm sure; and there are still areas where even more problems keep arising. More suggestions are always welcome, including ways to get around what currently seem to be problems.