You are correct that ETI may have evolved in ways or gone
beyond us so that our searches via radio and optical will be
fruitless with them.

But that is the problem. Since we are nowhere near the ability to
send out star probes to explore the galaxy, the only real methods
we have to search for them at present are through picking up their
signals and other noise made by technological civilizations.

If they use some incredibly advanced methods or non-technological
means to talk with each other, we are out of luck at the moment.
So we go with what we have and hope for the best.

Another hope that is just starting to take off is searching not for
their deliberate signals but for signs of astroengineering projects,
such as Dyson Shells.

To put aside for a moment whether any ETI would actually go the
routes we have envisioned for such advanced societies expanding into
the galaxy out of necessity to maintain their growing civilization, I
often wonder if we are seeing large-scale projects in our Milky Way
and other galaxies but cannot recognize them as such, or that most
astronomers who would like to keep their jobs wouldn't dare question
a dimming sun or a rearranged galaxy as anything but natural?

In the case of galaxy NGC 5907, some have speculated that its unusually
large amount of what are assumed to be dim red dwarf stars aren't a
natural phenomenon at all, but signs of a galaxy undergoing change
by a Kardashev Type 3 civilization utilizing the full energy capacity of
millions and perhaps billions of stars in that galaxy.

For some examples to the above, see the Dyson Sphere Search Program
at Fermilab:

http://home.fnal.gov/~carrigan/Infrared_Astronomy/Fermilab_search.htm

And Lu Arnold's speculations on ETI signalling the galaxy with huge
artificial geometric objects transiting their star:

http://www.obs-hp.fr/%7Earnold/homepage.html

For even more methods of interstellar signalling, see this online paper:

http://www.coseti.org/lemarch1.htm