I see three basic problems with traps. Forgive me, I'll probably be repeating others some here. Its just easier for me to keep my thoughts straight this way.
First is trap finding itself. Its pointlessly time consuming and needlessly restricted to a single class feature. What is so different about finding secret doors that anyone can do it, but no one can find traps without special training? I'd say make everyone capable of using Search to find all traps. Further, allow passive searching with a -10 to the skill, -5 for only moving at half speed. To replace the exclusivity, the Trapfinding ability removes the penalty for passive searching. (Alternately lessens it by 5 and add Improved Trapfinding at a later level to eliminate it.) That deals with the idiocy of people poking every 5 foot square as they travel at the awe inspiring speed of 30 feet a minute! It makes Rogues less essential, while still being useful for the task. Active trap searching can be reserved for obvious locations. Like that sealed off, uninhabited, Pharaoh's tomb, where they serve instead of monsters.
That traps do not scale well is the second issue. A big part of why is traps continue to focus on bland damage. A trap's purpose is first and foremost area denial. The secondary function is resource/manpower depletion. Traps in D&D almost exclusively focus on the second. The Trapfinding ability testifies to this mentality. At higher levels traps need to focus more on the denial aspect. Alarms are useful, if sufficiently difficult to bypass, at every level.
The single largest issues traps have though is simply they are usually misused. DMs wind up with bad habits in trap placement thanks to game developers providing poor traps and using them poorly in modules. Traps don't belong in the middle of heavily traveled hallways or in the middle of a cavern. When you place an automated trap, you place it where you never plan to go again. (At least until some sap triggers it and clears the place for you.
) They belong in baited locations, out of the way, or in sealed locations you never want to see again. Traps in inhabited areas should be safe until someone knowingly triggers them. The traditional method of salting every damn hallway in a dungeon loaded with monsters is just pants on head retarded.
With the right kind of traps in the right area, traps can become encounters in their own right or serve as an extra complication on another encounter. Making the trap itself obvious, but its trigger impossible to find or disable can serve as a nice area denial device, the modern minefield is a perfect example.