How much does it add? In terms of Hp, not sure - never got a dyno.
Yes, it's worth it to me now just from the performance aspect, but the money thing wasn't an issue. I saved up for it, then did it all at one time. The installation costs were included in that $2800 - all parts & labor for the shift kit, internals upgrade, TC mod & transmission cooling.
If I never go FI, then I don't think there was a need for the cooling system or the torque converter. The internals upgrade and shiftkit or valvebody upgrade would be more specific to staying NA. If you did a stroker kit or new cams and nitrous or water-meth injection, I'd probably do the other transmission mods to be safe. There are also torque converters specific for NA engines. All depends what your end game goals are. All of mine have been made with FI in mind - but with the luxury feel. That's why I kept the tranny ECU and why I modded the core TC instead of replacing it.
You could look into wire tucking your engine bay. That's a DIY that will take a little research. No performance, but it looks good! Paint your upper plenum, paint some of the plastic OEM reservoirs, replace plastic harness clips with metal P-clamps... lots of projects for the sake of projects. Might scratch your itch to stay involved with your car and save you cash at the same time.