Re: Fix up the Fatboy or get a Street Glide?
IMO, you are going to be in the same situation with a stock street glide. I rented one, no upgrades to it all stock. Now did I enjoy the ride absolutely! No questions asked, but it was begging for some upgrades (I rode 300 miles or so with a passenger on back who was light as a feather and no luggage).
If engine responsiveness is your only issue with the bike then start investing in some Stage 1 work, fuel management, air flow, pipes. The only way you are going to get a Glide or anything that you are satisfied with out of the store, is if you go up to a CVO and then you are talking about some serious $$$$, and you probably will still want to do some work to it to tune it just right. Harley's don't come from the factory tuned for performance.
Your call, but I would say if you like the bike you got, then just start some work on it.