Will I improve the qualitry of sound?

Somtimes the smaller amps are the sweeter sounding because there are less parts in the amp. The bigger amps will give you more volume. The music may have more ease and less strain even at lower volumes. If you are not pushing your volume control very far with your current setup than it may be all that you need.

If you are trying to achieve a better sound you may want to list your other components, perhaps you have another weak link that you are overlooking. I doubt the bigger amp will sound much different at normal listening levels. A speaker with a higher sensitivity will require less power to drive, give you more volume and result in a totally different sound.

Don't rush into anything.
Good luck!

If you are not doubling your amps output it may not make a huge diffrence, now going from 70 watts to 200 watts would make a diffrence but Stue is right on about small simple and sweet.