This is an old thread so I'm not sure if I actually posted already. Anyway, for me it depends mainly on two things. What I listen to and the room I'm listening to it in. Since I am addicted to both electronica and classical music which has a lot of deep bass content and I have a large treated room and listen at the outer edges of midfield, I like my system with subs. So much so that the speakers I ultimately chose have their subs built in and powered.
Some things to think about as to why deep bass can be important. I think I fall in the same corner as most people that would prefer no bass to lousy bass. But what about great bass?
Psycho-acoustically deep bass carries venue size information in the form of long LF decays. If one of your goals is to "be there" as opposed to the easier "artists are in your room with you", having it makes the suspension of disbelief much easier to prolong and maintain because getting linearly to the 20s helps a lot in setting up a spatial context.
Given proper drivers, low bass needs either a huge box and little power or a small box and lots of power. For those that can't have huge boxes, subs just might be the only solution. It's also important to note that big boxes and big drivers don't automatically give you bass in the 20's +/- 0dB, that has to be designed in. For example professional subwoofers used in theaters and concerts are designed to give massive output power only into the 30s. The large venues themselves create the very low bass via reverberation. At home you're not after raw SPL but rather (hopefully linear) tactile extension. In a small space you have to create the deep bass. Your room won't make it happen for you.
As with all things subjective, preference rules. It could be important to you or not. It is for me.