So how many people are using subwoofers

with full range floorstanders? I need just a little more bass weight out of my system and have vascilated between REL subwoofer or upgrading my amp from Conrad Johnson MF-2200 to an MF-2500. 60-70% of the music doesn't need a sub,but that other 30% keeps me off balance. Is the amp upgrade going to give me more bass weight (along with other benefits) or should I just go for the sub? I think I know the answer but would like to hear other opinions.
existing system=
CJ PFR pre
CJ MF-2200 amp
Theta Miles cdp
Silverline Sonata speakers
Homegrown silver lace ic's
MIT-2 bi-wire