Thanks to both of you for your very helpful feedback.
The purpose of the car is to be my daily driver, but I plan to make a hobby out of it as well, if/when any extra money comes around. I have two kids and a wife who loves her makeup, so I won't be socking away thousands into it at any one time, but maybe an exhaust here, headers there... nothing too extreme, yet anyway.
So I just got back from the test drive. When the guy pulled up in it after having just washed it, it was stunning to watch it roll up... the perfect combination of color and wheels in my opinion, and the paint was glossy everywhere, with only 2 main painted-over rock chips that caught my eye.
The leather looked like in really good shape, I couldn't see any cracks and definitely looked less worn than expected. I didn't think to look too close at the carpet (I took the wife and 2 kids with me so I feel like I may have overlooked a lot; I plan to look it over more intensely before I pull the trigger), but I don't remember thinking "Wow this is trashed". I did notice it looked like someone had an obsession with dash shine, as there was buildup around the letters on the passenger side dash. The interior could use an actual cleaning wipe down, but it all looked in good shape.
The tires were probably 50%, but F/R brakes were replaced just 6k ago. The service record was pretty thorough from about 50k on (the guy bought it @ 27k), with around $5k spent doing mostly fluid maintenance, and intake manifold replacement if I remember right. The engine compartment didn't have a nice recent detail, but it did look "clean" and I didn't see any evidence of leaking.
What did surprise me was the ride/transmission/clutch, and I'm hoping maybe someone can comment on this. It's probably important to know that I've been driving an automatic 2005 Civic VP (75k on odo) for the last 3 or so years, so I'm used to a very light, zippy, tight-ship vehicle. I have no reason to believe that this mustang is in anything other than great shape, I just haven't yet test driven another similar mustang to compare it to to see if these things are common/standard or not. But, I first noticed that the ride was somewhat rough (all this is compared to my Civic), and rough areas of asphalt made it feel like the shocks/struts needed replacing. Also, the clutch travel seemed very stiff and long (
) , with a very sharp engagement point just barely off the floor. This, combined with a stock shifter, made it hard to imagine smoothly and precisely shifting through the gears to achieve any sort of sustained acceleration. Can this all be chalked up to the fact that it's a heavier and/or stiffer car, and I just need to get used to the way it shifts? I haven't driven a stick for 3 years, so that could be plausible.
As far as the clutch goes, I didn't notice any slipping under heavy acceleration, and I tried something my dad taught me (effective or not?), to put it in 4th or 5th at a dead stop and pop the clutch to see how quickly the engine stalls. It pretty much stalled instantly, so I'm guessing the clutch is still just fine. Overall, it just didn't seem like such a tight ride as my civic, and maybe that's just because I'm (ridiculously, I know) comparing apples to oranges, and the fact that the car is still 10 years old. Despite all this, I'm not at all saying it wasn't fun to drive... I'm just used to a tight and responsive car, and I'm wondering if I should expect that from an 03 mustang in great shape, or if the ride I experienced is just what comes with an older, heavier car.