Why the fascination with subwoofers?

Thanks @mapman 
I am not necessarily looking for affordable but rather something that would be absolutely transparent since I would be high passing the entire signal above 40 or 50 Hz that is going to my main speakers.  That is one reason I have been curious about the Vandersteen model since I suspect it is about as transparent as these things get and plus it is simple, and another plus is that it is balanced, which is how the cabling is in my system.  I have thought about the Marchand units and they do make a balanced passive unit with poly caps and "high quality" inductors, at a reasonable price but I have not pulled the trigger since my roll-off/hand-off at around 40 Hz seems to be working and my amps are powerful enough that inserting the crossover might be creating issues to solve an issue that doesn't exist.  Maybe I should give one a try just to see. 

@mitch2 ,
I am glad you are considering the Vandy subs.
To me, they are the best way to add lower frequencies to a speaker- A simple 1st order crossover that eliminates frequency overlap and allows you amp to function at peak performance.
Once I sell my 2w and 2wq subs, I will be getting the new Sub 3 model.
Bob

I match a pair of Paradigm Servo 15's with my Apogee Duetta Sigs to pick up the 30 hz below the range of the Sigs. Sounds great on all music genres and did not cost a fortune. Got them used on Agon.

Sub(s) make listening a fuller richer experience. Even when not optimally placed they help. They don't take too much messing about to get them sounding/feeling right. 

For watching movies with explosions then a big and loud sub(s) add a lot. For music more nuanced is all that's needed. 

For young men in cars it's essential to have one that annoys other drivers and people in their houses. Not!

...and then, there are the few of us that do not have the financial means to afford such all-inclusive systems and add sub-woofers in an attempt to add depth & resonance (due to inferior equipment) for more listening enjoyment. We make due the best that we can.