I own KLF-20 and RF-7 Klipsch speakers. I've also had the Forte II Klipsch speakers and the KLF-20 were on the thin side compared to the Forte's that kind of really bugged me, nice sounding but thin compared to the Forte and RF-7 but I replaced the diaphrams with the Titanium kit and this helped the KLF-20's not be so thin sounding.
The RF-7's are smoother and all the way around better from top to bottom than both the KLF-20 and Forte II. I've heard the RF-7 sounding just ok, to absolutely stunning sound by just what it's run on, so the equipment you pick for it is very important as the RF-7 are very dependant of what sound you get with just how good of gear you run on it. Give the RF-7's the best quality and it will give you back stunning nirvana sound like no other, the RF-7's perform better than my 1995 Klipschorn's with imaging, resolution, and detail. The Klipschorn's have a larger soundfield but the RF-7's come darn close to it.
My KLF-20's are from 1996 and I've never had any problems with them and the build quality is pretty good for todays speakers but yes, the build quality on the RF-7's are better.
Klipsch speakers are not bright unless you put a bright source to them. The trick with any Klipsch speaker is to not put a bright source with them because Klipsch is VERY revealing speakers.
The sound from the RF-7's are stunning and the crossovers DO NOT need to be changed, run them with very good quality high current gear and you will get great quality sound. People who changed the crossover are doing it to tame down the sound when using it with bright gear. I don't recommend that because it takes out the "presence" that is so revealing and involving that the RF-7's have.