1) It's personal preference. If you're the "if it isn't broke don't fix it"-type then leave well enough alone. If you're the "need to have the latest and greatest"-type then sure, download the most recent revision for each & every driver/utility.
2) Uninstalling the older version prior to installing the new version is usually the best route if an uninstaller option is available. If not, just install over the existing. Outright deleting it is generally not a good idea since you may miss something or accidentally delete the wrong file/driver and end up causing more harm than good.