you should now that a reflash is the solution for 99,9 percent of your n900 issues.
but it takes a little bit time and you will lost all your data.
the repositorys can make your phone laggy,weird,crash,reboot,data corruption,lose some other phone function and make your phone totally unstable.
but not all devel/extras apps are evil.
i would read the updating your firmware wiki and after you are good with flashing give it a try.