As a core design philosophy I am 100% with you. But it must be applied in a thoughtful, case-by-case manner.
As annoying as it may be (that's a lot of work), BryonD is correct here.
But, if the wizard is invisibility, he can not be seen, sneaking or not. Does that give the wizard a huge advantage in sneaking? Yes.
However, not being seen and not being
detected are wildly different animals. Myth, legend, and fiction are filled with examples of people detecting the presence and approximate location of invisible beings. The methods vary, and it is never frequent, but the precedent seems to provide a guideline for us to follow.
Oddly, I actually
like the OGL invisibility rules. Under those, invisible characters are (excepting serious noise on their part, or counter-magic on the defender's part) undetectable further than 30 feet away. Within 30 feet, it is a DC 20 / 30 Spot/Perception check to note that a creature is nearby, and a 30 / 40 to note exactly where it is; this allows even a commoner to locate a (lazy) invisible creature.* When forced to actually hide, being invisible provides a massive bonus (+20 to +40) to checks; enough to counter the "hiding while attacking" penalties. So far, so good.
My issue is that not enough people understand them and use them correctly.
Does Spider Climb harm your game? If spider climb provided a +10 to climb checks, would your game be better? ... But I don't see that you have increased fun.
Why not have
Spider Climb only provide a Climb Speed? That gives a +8 to Climb, take 10 under stress, normal defense while climbing, and lets you move at the indicated speed
as long as you succeed at climbing. Now the Rogue with spider climb is better at climbing than the Wizard with spider climb, though both are pretty freaking awesome (Str 8 Wizard still has a 17 Climb that lets him traverse many surfaces). Then slap a DC on perfectly smooth, flat, vertical surfaces (around 60, maybe more, trying to retain that "impossible! Unless you're epic" feel) and you're rocking out.
Of course, you've decreased the Wizard's fun some, since now he can't climb on most dungeon surfaces (removing the "I'm Spider-Man!" effect) without actually knowing how to climb.
Knock I can actually see as a good choice. When the spell is cast upon a locked item, any lock, even magical, may potentially be unlocked and the caster (or secondary target if you rather) gains a +10 to Disable Device. That works for me.
Me too.
*Concealment is way too effing good. All my military training emphasized the value of cover over concealment, because cover will actually stop bullets while concealment just means the other guy is trying to get lucky. Cover means that lucky (or aimed) shots will still miss because they can't punch through the cover.
OGL concealment is the best damn thing ever. 20-50% immunity to all attacks, including critical hits. Only total cover can compete, and that's
only if it doesn't allow the attackers to target you (directly or indirectly).
This is bad from an immersion standpoint (which I've already hit upon) but more importantly from a
fun standpoint; I've lost track of how many confirmed critical hits I've seen miss because of concealment. In every case, everyone at the table (even me, the rat bastard DM that enjoys killing PCs because it means I'm winning [bad habit, and one I'm breaking, but it's still true]) thought that was weak-sauce.
An alternative rule would be very welcome.