RMS power is probably about 5w, MAX power is around 10-15w. The rest of the specs don't really matter. Just about any aftermarket headunit over $100 will sound better and put out more power.
When it comes to upgrading, you should do one of three things:
1) Buy a new headunit AND new speakers
2) Buy an external amp and new speakers
3) Buy a new headunit, external amp and speakers
Simply put, the factory deck doesn't do a great job powering aftermarket speakers which are designed to handle 3-10 times more power.
*NOTE for option two above you may need a line-out-converter if the amp you choose does not have speaker-level inputs.