SPOILERS AHEAD

If you ever listened to the Penny Arcade/PVP D&D podcasts, in the third series starting here, the DM Chris Perkins ran a dungeon similar to the Tomb of Horrors but didn't spring any of the traps until the party was already deep inside the area and had collected the treasure they had gone in to find. They then had to go through everything on their way out. This gave them a false sense of security as they only had a few easy encounters on the way in that they fought through or snuck around but had incredibly difficulties after an enemy NPC activated all the traps.

This might be a good way to revitalize the Tomb of Horrors and make it fresh. Obviously YMMV depending on 1) how much knowledge your players have of the original Tomb of Horrors and it's layout (if you steal it directly), 2) whether they've listened to those podcasts before, and 3) whether your players would tolerate you trying to murder them after they thought they were safe.

As an aside, I would highly recommend listening to the Penny Arcade/PVP D&D podcasts. They don't always play by the official rules (they sometimes get rules wrong though generally not on purpose) and aren't the most serious of players but they always have a really fun time and they are very entertaining. Chris Perkins from WOTC who DMs most of their campaigns is a very entertaining and ingenious DM and you can steal a lot of good stuff for your campaigns from him. You can find all their podcasts here under the Acquisitions Incorporated heading. The very first one starts here