A lot of people (especially the ones here) arent going to like this. But a creative person will never (or at least not for a very long time) get bored of vanilla. Look at Etho
I strongly disagree with this. There is a very large plateau when it comes to what you can do and create in vanilla which is based on the fact that in vanilla the only gains in efficiency that you can realize are ones through parallelization.
Take a simple example of smelting. In IC2 you get gains both in time and material through the furnace->iron furnace->powered furnace->induction furnace line. The same for TE with furnace->powered furnace->induction smelter. The higher machines require more materials to make, but return by being faster and/or burning less fuel to perform the same operation.
Now, if I want to smelt something faster in vanilla what can I do to increase efficiency? I run multiple furnaces in parallel. That decreases the amount of time it takes to smelt large batches of items but does nothing to decrease fuel use. No amount of creativity on my part will alter that fundamental fact of Vanilla.
The same goes for automation in vanilla prior to 1.5.x. There is a hard plateau that you cannot get around. We didn't have a method of injecting items into an object aside from doing it yourself. The most automatic we got out of vanilla was water. We could auto-harvest and move items around with water, but not actually plant anything nor gather items without being present.
In 1.5.x this changes with the hopper, but it is barely a step above what we got before. We can now auto-gather (water pushes into the top of a hopper) and queue up larger and/or varied batches. But we're still doing much in the way of "go here, grab this, place it there."
Because of this relatively low plateau as well as minimal number of interactions it doesn't take someone long to first hit those plateaus in efficiency then hit the plateaus of automation. From then on it is simply a matter of cosmetics; and
while people can do some awesome things when it comes to cosmetics, I think it is disingenuous to imply that people who are more interested in mechanics over cosmetics are somehow deficient because they hit the comparatively low mechanical plateaus in vanilla and find themselves out-of-sorts after having experienced the wide vistas of mechanics that the mods offer.