As you say, there are some skills helpful at the start of the game which you may not use later, but I personally found level 1 of Healing to be useful even late in the game, though not needed very frequently. I tried Battle Rage, for example, which did help, but I only used it a couple times, so when I reskilled after getting the battle tower, I didn't bother relearning it. At that time I maxed Potion Efficiency, thinking that would help, but I didn't really need it, so the second time I unlearned my skills I didn't bother relearning it.
It is also possible to switch from using a two handed weapon to duel wielding, or vise versa, etc, and depending on your stat distribution it may be possible to make more drastic changes to your character build (an Intelligence based warrior could pretty easily switch to a mage, where a Strength based warrior could have difficulty, requiring charms or a few levels worth of stat points to bring Intelligence and Spirit up).
After you get the battle tower, about half way through the game, you will be able to raise the level cap of most skills (Lockpick and Mana Efficiency only have 5 levels, for example, so there are no upgrades for them). There are a couple stages for the upgrades, for increasing amounts of gold (the first can bump the level cap up to 10, the second up to 13, or so, depending on the skill).
