You can load a 1.04 save to 1.05 beta and keep playing with the new changes. You'll get the UI improvements, the class balances, etc. Some changes aren't retroactive, like the PER <=> INT switch from the Grieving Mother, the Personal Records lost when swapping characters, or the ability to respec companions when you first get them. In fact, there is a game breaking bug going on right now that will prevent you from properly recruiting any 1.04 companion in a 1.05 beta save due to Character Sheets getting bugged. This might get fixed in the final 1.05 release.
It's up to you to apply the patch or not. Personally, I'm going to wait to make sure everything is in order then start a new fresh game.