If you measure performance only in terms of numbers on an SPL meter, then sure you can get much more for much less. If that is your measure of performance then you really aren't JL's target market anyway.
You can get a ton more power than McIntosh, Tru, Genesis, Sinfoni, Audison etc... for much less money but everyone who goes on and on about how JL is overpriced drools all over those brands which in reality are nothing all that special.
A lot of people don't like the sound of the W7, but a lot of people don't like the sound of the XBL^2 subs either. I've never heard a legitimate complaint about the quality of the output of any of the other JL subs only about the quantity. They do OK on output for an SQ oriented driver and for the person who wants to listen to music (not just rap) on a quality setup at sane levels, the JLs fill the bill very well.
You pay some for the name, but most of what you pay goes to the in house R&D that JL does. What has Kicker done in the way of innovation in the last 10 or so years? They change the look of their subs every year but that's it.
I've got a JL sub that is 16+ years old. I got it back when they were about as mainstream as Ascendant or Fi or Stereo Integrity are now (yes the people on here know those brands but ask some Joe off the street and chances are they've heard of Kicker, JL and maybe MTX but not AA, Fi or SI). JL earned their reputation as one of the best subs on the market and built their market share and name recognition through performance. They did it before there was an internet and they did it with minimal advertising. Look back 15 or so years at every head to head comparison of subs in the car audio mags and you will see that if there was a JL sub in the comparo, it won. It wasn't because they spent a lot of money advertising in that mag either, because, like I said, they hardly advertised at all. The best advertising for them was done at the IASCA world finals where they had several winning streaks that spanned years.
The real answer as to whether or not they are overpriced is sales figures. I don't think that they are having trouble moving product...