If you are only flying VFR the GTN 750 is overkill. Replace your Comm 1 with a modern Garmin SL40 Comm and buy a good portable moving map GPS unit. You will probably find that after you get used to the kit you will never look at the rest of your radio stack.
If you are flying IFR then yes the GTN 750 is the way to go, but be prepared for an eye watering install bill as the radio shop will have to rewire everything