When it comes to searching, I am much in favor of 3e's approach
1. If the players search the wrong area, they find nothing (I will still have them roll).
2. If they are very general, I will give them a roll.
3. The more specific they that they are I will give them a bonus of +2 to +20 (DMs best friend).
Depending upon the nature of the action, this may just lead to clues. For example, searching the book shelf might reveal dust in front a book (which needs to be removed to open the secret door). Searching the proper section of wall may reveal the presence of a secret door, but not how to open it.
4. If they do the exact thing necessary to find something, then no roll. Pulling the correct book (even if the player states they are pulling all of the books) off the shelf (or pulling on the the sconce) will open the secret door if that is the trigger mechanism. Searching under the bed will reveal the chest. Unscrewing the cap on the bedpost will reveal the map if one is hidden. This is really no different than the discussion in the DMG about having specific actions required by the characters to move the levers in the correct sequence to open a door.
When it comes to diplomacy, bluff, etc. I prefer the characters to act it out and the roll follow. Then the dice roll represents how effective they were. The player with a low charisma or low diplomacy character may have a good point, but somewhere between his thought, the words leaving his mouth, and the message reaching the listener something went wrong if the roll fails. Maybe, it was the words chosen, used the wrong tone or spoke out of turn and the message was lost. I might even give a bonus to a higher skilled character if they pick up on the actual point "What my friend was trying to say..."
And I have no problem splitting the party. Sometimes, it is necessary. So, the group can't always rely on the best skilled character (or the back up) to always be there.