Owning a mustang and being happy is actually very simple. If you're not happy, then the car isnt for you, simple as that.
As far as your suspension, I dunno where you shop, or who you talk to, I dont really know anything bout ya heh, but, I know these cars can handle...if you put up the effort and time. It's no more expensive than any other car really...I got my older one to handle as good as my '97 VR6 GTI, which had full coil overs FK silverline to be exact, total suspension and brakes systems cost me around 3k, and my stang handled damn near as good, so, it can be done.
Sounds to me like you're just sick of the car. Take it off the road for a while, that is if it's not already, and let it sit. If you dont start to miss it after like a month, or if it doesnt make you happy driving it after so long, you've defonantly grown numb to the stang.