55-250mm type lenses do have a good purpose, yes they are not the sharpest and are a compromise of cheap and covering a long focal range; however they are smaller, lighter and serve a lot of focal lengths to the user. They are ideal for one lens does all occasions when you want to take the camera, but don't necessarily want to or find it practical to take multiple higher quality lenses (heck I know of several professionals who use these lenses for scouting out potential shoot sites).
I wouldn't ditch them, but I would put a mind to considering some new glass, you'll see a massive increase in quality with good quality lenses and that will make a big difference to your photography. Further if you've the mind to go for a 5D in the future then looking now at EF lenses is worth while.
If I were you'd I'd do the following:
1) work out a rough budget - nothing set in stone, but a number on the table
2) work out what you want from a new lens; what situations you work in, what focal lengths you like using, what types of subjects you are working with and what kind of photos you want to be able to take. This is putting your criteria on the table and is essential for finding any product that you want for your own use - otherwise you'll just get random lists of other peoples top choices.