Simple question......Is there a mod that allows for increased spell durations & magnitudes, similar to one of the settings in the "Morrowind Code Patch"?

http://www.tesnexus.com/downloads/file.php?id=10763 does that. You have to edit Oblivion\Data\menus\prefabs\darn\enchantmentsetting_config.xml to change the defaults (details are in the file).

edit. added link

If you don't want to use any kind of UI overhaul, you can use http://www.tesnexus.com/downloads/file.php?id=2917(x3) or http://www.tesnexus.com/downloads/file.php?id=17284.