I think the Knowledge skills are useful enough, if applied, and generally general enough... I think that's the lack of skill points does make for ignorant, incompetent PCs, however. There are lots of ways to fix this, though.
I like skillful, competent PCs, myself, so I allow all characters their full skill points, as well as (4 + INT Bonus) Racial Background Skills/15 years of age, x4 at first level. Huamns get +!, and Half-Elves/Half-Orcs get +1/30 years. While Dwarves & Elves seem to clean up, at first, the Huamns and Half-Humans really do... Anyway, these points can ONLY be spent on Racial Background Skills, which always include some Knowledge skills, Crafts, Professions, and Performance styles.
After CharGen, all classes get +1 Rank/level in all of their class skills. This means that, once a skill has been maxed out, that it will remain maxed out, without needing to keep further track of it... It also means that all classes have all the appropriate Knowledge skills, as well as AT LEAST one Craft and Profession/level (except for the poor Fighter)!
In addition, five Ranks in Knowledge (History) gives you a +2 Synergy Bonus to Bardic Knowledge. I allow this to apply to ALL PCs, whether or not they have Bardic Knowledge. ANY Bard will always be better than them, in this, but if there isn't one in the party, the knowledgable PC can at least try, with a +2 bonus, where no one else can.
Also, Rangers with an appropriate Favored Enemy are always treated as being skilled in the appropriate Knowledge skill, even though it may be Cross-Class... For instance, a Ranger with Favored Enemy: Orcs at +2 is treated as unskilled in Knowledge (Local), except where it applies to Orcs, then he is treated as skilled, and gets +2 on the roll. The same with Knowledge of Orcish society, etc. Likewise, a Ranger with Favored Enemy: Humanoids (Evil). A Ranger with FE: Dragons is treated as unskilled in Knowledge (Arcana) for purposes of recognizing magical goodies, but as skilled (with his FE Bonus) for anything having to do with Dragons.
Also, I would add Knowledge (Architecture & Engineering) and Knowledge (History) to the Fighter's skills. When the Captain orders the men to the merlons, or to the murder holes, they need to know where to go... Also, Knowledge (Engineering) should allow Fighters to operate the Siege Engines, using THAT skill, instead of BAB to hit. Knowledge (History) mentions that it covers ancient battles, and therefore covers the knowledge of both Strategy and Tactics that so many DMs seem to want to add... Besides, Knowledge (History) eventually gives that +2 Synergy Bonus to Bardic Knowledge, and many old Fighters historically became Bards, so this seems to fit, to me...
Knowledge (Engineering) covers a lot more ground, in my games than it seems to, in many... Any time that a PC wants something new invented, they will either need this skill, or money to hire someone with it, to draft their new plans. New devices made without it may have certain... "oddities"..., and not operate quite as expected...
Also, as mentioned, there can be a lot of overlap between some Knowledge skills... Knowledge of a certain society may fall under (Geography), but also certainly under (Local). When down in the dungeon, a statue may just be a statue, to most, but Knowledge (History), (Local), or (Nobility & Royalty) might identify who it is a statue of. Knowledge of (Arcana) or (History) might give hints as to the demise of the ancient Suel kingdom... Etc.
ALL of these methods, taken together, would give a MASSIVE boost to PCs (and many might argue "too much!"). Any of them would yield a slight boost. A few, in combination, would strengthen a few classes.
In any case, there are enough Knowledge skills, and no need for more... Knowledge (Tactics) should go under (History). Knowledge (Psionics) should go under (Arcana), or perhaps (Nature), if you want to use "Psionics are Different". Knowledge (Astrology) or (Astronomy) should go under (Nature). There is no need to be adding more...
Now making USE of the Knowledge skills, during the game, is up to both the GM and the PCs. MOST of these skills give knowledge of the capabilities of SOME sort of creature, and ALL of them give a Synergy Bonus to SOME ability (even if it's one the PC doesn't have). Allowing 5+ ranks to give that ability might also help make PCs want to take those skills, at least a little... The ability to answer DC:10+ questions already does!