Is a Sub worth the bother?


I have a small, simple system that pretty much meets my listening needs. It's an NAD C715 (all-in-one deal) with a pair of Epos EL3 bookshelf speakers. I've been kicking around the idea of getting a cheap subwoofer with the idea that it would add a little oomph to things. This is strictly a music system, not home theater. I guess my questions are: 1) would a sub help that much or am I just limited because of the EL3s? 2) If a sub would help, would a cheap one be okay (I'm thinking along the lines of the Dayton sub 100, perhaps an Energy Take Classic 8--$100 at Costco these days). My room is roughly 12 x 20, but again, I'm not looking to bring down the house/neighborhood.

Thanks in advance for your thoughts.
comfortstarr
I'm enjoying my first sub which is cheap, and in my opinion, fairly good. It's a Polk which was barely over a hundred from bb on a half off sale. However, it seems to underpin my monitors nicely and add something i've definitely been missing. It's not the most articulate thing I've ever heard, but still adds considerably to listening experience.
The kit from Parts Express is tempting. Do they ever go on sale (it's $399, but several of the reviewers mentioned getting it for $300)? There are a couple of subs in the classifieds section here close to my price range one by Elan and one by SVS. Anyone know anything about those brands? I did a little research, but didn't turn much up (especially on the Elan).
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.