Why more economical? Why would a new system be better?
Because from how I understand your system, your speakers are run by your subwoofer which is connected to your amp? The speakers are connected to your subwoofer? If this is the case, if you wanted to upgrade in the future, you are governed by your sub. If you sell your system now, you will get a premium price for it - a couple of years down the line, you won't get much at all. You can get good deals when buying a full system.
As for why it would be better. My brother-in-law had the Acoustimass 15 or whatever it's called. He paid £2k plus for it. He then sold it and bought the B&W MT20 plus a Denon 2808 for less money. The difference was evident immediately. If you then think that traditional speakers give you better bang for your buck than style speakers, you would have to go very wrong not to get a better sounding system.
At the end of the day though, it is up to you what you buy/sell/keep. Good luck.
CA 840A; Sony BDP S550; CA DacMagic; MA RS6AV with Radius R90s; Sony KDL40W2000; Sony STR-DA3400ES; Sky HD; Linksys DMA 2100; Chord Chameleon Silver Plus RCA; Chord Chorus 2 XLR; Chord Odyssey 4 cable; QED SR hdmi and Clearer Audio Silver Line Coaxial.