Also it's likely that advanced civilizations don't need artificial light, or much of it. I don't think it will be more than 200 years before the dominant lifeforms on earth aren't biological. IMO non-biological beings will have far less interest in the physical environment. That is, outside of energy production, their universe will probably be more internally-focused. So, if you consider a 300-year window that we will be lighting up the earth at night, chances are that we won't catch anyone in that slice of history.
I read an article 10 years ago that said "well duh lasers are passe we should be really looking for pulsed microwave emissions." It might have been Seth Shostak who pointed out that SETI is one of the most "fashionable" sciences, in that it's driven by whatever the prevailing fashion is at the time. Percival Lowell, for example, was looking for canals on mars not just because he didn't bother to look up the Italian word "canali" but also because big damn canals were the engineering marvel of his era. So yeah. I'm right there with ya when you point out that this article is about looking for space LEDs. At the same time, it's a "free" search. You don't need extra gear and you can piggyback on existing or proposed telescope missions. There are two parts to observation: "what are we looking at" and "what are we looking for." The "at" is booking time, but the "for" means "which instrument package do we strap on" at worst. I read an interesting article in Scientific American a couple years ago about searching for extraterrestrial flora. The author pointed out that with next generation scopes we could theoretically be able to detect life on other planets simply by looking for that star's equivalent of "chlorophyll green." The trick, according to the article, was in knowing what color that would be depending on the star. It's all spectra, after all. It just depends on what you do with it.
One thing that really excites me about SETI are the possible surprises that await us. If we are lucky enough to detect other intelligence out there, I am certain that we will have to do some serious reassessing of our current situation. That's why even though this hypothesis seems misguided, I am all for collecting more information on extra-solar systems and planets. Every bit of data is a clue, and we'll probably find valuable information where we didn't expect it. Even the lack of a signal is good data.
It is interesting that SETI just looks at the hydrogen line frequency. At least they did last time I checked. http://www.setileague.org/askdr/hydrogen.htm But IMO the reasoning for that is a bit better than city lights.