I would give the same advice as "someone". First you should upgrade your speakers to sound good and to your preferred loud. Then upgrade to subs do both at the same time.
Woofer is a small part of the system, most music will be coming from the speakers, even the midbass should be coming from the speakers, the woofer will only be used for low freq bass.
But that's my opinion, most people do the reverse. It's all about personal taste. Some people are happy with just bass and could care less for the rest of the music, for those people the "someone" gave advice that wasn't important.
You just need to distinguish what's more important to you first. The bass or the mids/highs.