Could I get a double check of my math on this one. Planning a Paladin with WIS 14:

Assuming I max the skill to 25, with a take20 roll I will heal at most 47HP (25 + 20 + 2) ... at a time when my character has like 240HP. Does that sound right?

yep. the skill isn't there to take over healing from stronger sources like rest, potions, spells, its a backup skill that you can use, plus can cure poisons and diseases along with healing. Your not going to become godlike with high concentration. you aren't going to become godlike with high healing skill.

Cure Critical Wounds heals 25 HP per use. With a +10 Healing Kit his paladin will heal 45 per use on average in the same timeframe, or nearly twice as strong.

In other words, Healing Kits are more effective than potions unless you literally have Potions of Heal. Though they do leave you flat footed while using them...but then they don't provoke AoOs like potions.

Finally, note that you can use healkits on other people. Quite helpful when you're a rogue or wizard with a tanky henchman.

It's even useful in multiplayer, where spamming healkits can help keep a partymember alive quite effectively. Perhaps it won't work in super high level/magic environments (where I never played) but it can be very helpful otherwise. Sure, you're no cleric, but you may not always have a cleric in the party. (And healing kits can't be interrupted.)