Is a Sub worth the bother?

A find subwoofers to be very important for speakers that don't go too low. They will often make an appreciable if not substantial difference to the overall presentation of the music with a more solid foundation. I concur with most thoughts here in getting a reasonably quality sub to augment the low frequencies of small bookshelves. You may not blow the roof off with the sub but you will tap you feet along the beat of the bass notes once you get a quality sub in.

I have a buddy that uses the SVS (2 of them)and he loves them, personal taste when it comes to subs. After going crazy with better than 10 subwoofers I have landed on what I feel to be one of the most musical subwoofers on the matrket, Rythmik Audio F12-SE. This is an internet only company so no overhead or sales people, rent and all the things that drive up cost. Probably more than you want to spend but worth looking at. Have you looked at the 8 inch Velodynes, the mini series, again a buddy uses one with B&W monitors and the sound is very nice. I think the key for you is to get a solid 8 or 10 inch woofer that will mate well with the monitors, best of luck.

Depends... what kind of music do you listen to? Most rock, pop, and jazz won't really benefit if your speakers will reproduce at least 40Hz. If you listen to a lot of classical and/or anything with a lot of piano, then it might. But don't go cheap. A cheap sub will sound horrible. You can pick up something used, but very good, for a few hundred and be happy instead of having a $100 sub sitting in the closet.

i'm unsure what most would consider a "quality" sub, but yes...adding a sub will help your bottom end if you're running short. am currently running a velodyne but have experience with boston acoustic and polk subs. in every instance, the sub improved the overall sound to my ears. i remember adding a no-name $59 sub to my sisters crap stereo 10-15 years ago. it was no where near as crappy afterwards.

a quality sub would obviously be best but a decent one will also help...when compared to none at all. if your mains don't reach low enough or are short on hit/slam, adding a sub is a good way to go imo.

Yes, it's worth all the bothering and sorrows and despondency which you will undergo through during its setup. I have AE Aegis Evo 3 speakers which go down to 40 Hz (-3 dB) and 36 Hz (-6 dB).

I added a second hand REL Quake sub and it absolutely transformed my enjoyment of music and brough it to another level. But integrating it into the system was a pain. I did it eventually, by ear first. The result was ok. But then I learned how to use software Room EQ Wizard and I found even a better place for the sub using a mike and this program. The result became excellent.

I also use the VST Oxford Sonnox EQ in Foobar2000 to smooth the remaining irregularities in the frequency response of the sub and the woofers (20-100 Hz).