I just made a comment about the "Dragon" in another thread and then came here and saw you speaking of it. IT is a blast isn't it? Hell, the posted speed limit of 30 MPH (I think) is tough to handle in some spots. The down side tp it is getting stuck behind grandpas in their Goldwing motorcycles going 15 MRH thru there. Anyway that is in my backyard and I love it. Great testing/proving ground for tour modifications.
On the suspension question....I am sure I will be told I am wrong but I will offer my advice to you.
I redid everything to my suspension. The BIGGEST IMPROVEMENT I noticed was after adding the new swaybars. I went with the STEEDA Front (which is a monster compared to the twig it replaced) and the STEEDA Aluminum Swaybar brackets (These are a little pricey and not that necessary but I went ahead and did them with the swaybar) and the STEEDA Adjustable rear sway bar (that goes on WITH your stock one-does not just replace it)
I put UPR coilovers on the front with Tokico Illumina 5 way adjustable struts and STEEDA Sport springs in the rear with Tokico Illumina 5 way adjustible springs in the rear. I also changed the upper and lower control arms in the rear to STEEDA aluminum height adjustable lowers and double adjustible upppers.
Also UPR bumpsteer kit and caster/camber plates.
I know that is a lot but it can be done in stages. I also wanted to be able to adjust everything-fride height and firmness-from drag racing to road courses to cruising. This allows me to do that.
I have a bunch of other crap but that is the main suspension stuff.
I did everything but the sway bars one weekend and noticed a good difference....but after adding the swaybars the difference was phenominal.
I believe the Bullit has stiffer/more aggressive suspension stuff from the factory and you said that is what you have but anyhow if I had just wanted a little better handling and look....I now know I would have just went with sportier springs and the SWAY BARS, maybe some stronger, non adjustable lower control arms. It would be nice to do better shocks/struts while doing the springs too but that depends on your funds.
Heck just try the Swaybars first. I know people will say I am full of it but I drove my car for a year stock. When I added those swaybars-it was like a new car. Body roll became almost non existent and grip improved greatly. I have a clover leaf close to my place that is my little proving ground if I don't want the full Dragon experience (Pellissippi Interstate and Alcoa Hiway interchange, if you know the area) Those swaybars are what made me realize the stock Mustang GT seats suck for lateral support
The two swaybars would run around $250 if I remember right (without the aluminum brackets). The back one is a bit of a bitch to get on....I could have used a few more hands to do it. If you live remotely close though I'd love to help you put them on though. IT was pretty fun to do now that I look back. Good feeling to accomplish something like that considering my most complicated auto install prior to it was brake pads or an oil change

Springs would be $200-$250 I believe and shock/struts around $500. These prices are what I recall paying for my specific brands about6-9 months ago.
Oh yeah 17X9 & 17X10.5 rims with 275/40 & 315/35 rubber are a hell of a lot of grip to add to your car too. MASSIVE GRIP. And looks mean-oh so mean too. That'll cost you $1500-$2000 though
Hope this helps a little.....Ken