The other side of EE is that, once you make it to the upper levels, you have tools that are far more effective than creative mode at allowing rapid construction. A ring for flight. Clearing up to a 64 (or was it 128) long 3x3 tunnel in a single click. Harvesting a massive area of trees. All of that still requires fuel, but another power item can absorb astoundingly massive quantities of fuel, so that you don't need a half-inventory of stacks just for half an hour of pre-megaproject terraforming.
On top of that, it adds a way to quickly place materials into flat surfaces (floors, walls, roofs), ways to destroy enemies, ways to take less damage, and, most importantly, ways to get just about any resource without having to specifically hunt it down.
So, it basically adds a lot of content past what regular minecraft would call the end of the endgame, allowing you to continue to the point that you have earned the equivalent of creative mode, and then beyond that.
Also, the condensers can be given a target item, and they will produce that specific item, if you give them the raw materials (fuel and a lower quality block to upgrade, fuel can be in the form of directly feeding it EMC, not just burning fuel items in it). This means that if you want to build a massive sandstone castle on a mountaintop in a snowy plain reaching as far as you can see, you don't have to carry each stack of sand from increasingly distant beaches or construct a vast rail network just to get the materials you need. Of course, once you have the machinery set up to get those resources, you could have carried in a full inventory or two, but what is more interesting, mining stack after stack of sand, or setting up and automating a system so that it produces more materials while you are building with what it has made so far?
Finally, storage. EE adds chests that can be placed next to each other without problems (as they don't combine into double chests), and can hold slightly more than 100 stacks. Or, for a higher investment, you can make one into a bag, that can be opened from anywhere. In fact, up to 16 of them, one for each colour. And if a bag is destroyed, it's contents aren't lost, as every bag of a certain colour links to the same magical inventory dimension, so all your stuff is safe, though you may need to seek out another two or three diamonds to get it all back.
Basically, an endgame beyond the endgame that can lead to a creative mode better than creative mode... And who can resist the power to rain lightning upon your foes and control the very sky itself so that the weather and even the sun and moon change on your whims?