Safe and parked outside: this tells me no convertibles. Bummer, because of the Miata, Boxter, and S2000 in particular
Reliable: to me this says naturally aspirated and possible to find one that isn’t thrashed. I’m sure there are some turbo cars that buck this trend, but in general my experience has been that most turbo cars seem to have a lot of thermal issues on track, especially ones with long straights.
No engine swaps or trailers: has to be somewhat civil on the street
Autocross potential: my class knowledge is so outdated I’m not much use here
Just enough power: at least around me, even with 200hp in an E30 I still end up driving in my mirrors depending on who else is out there. There are just so many modern attainable cars that are absolute rockets in a straight line.
Easy on consumables and No Unicorns: makes sense
An E30 of course is my pick, I love them on track and have tens of thousands of miles doing so in them. You’re not going to get 200hp without a swap or boost though. A 325i is around 160 crank horses stock. My turbo 318is was good for around 240 crank horses, but reliability was never as good as I wanted it to be.
E36 328 or M3 would be way high on the list, still cheap consumables, very common, gets you into that happy 200hp ish range. And they’re still cheap to buy a decent one. E46s are similar story.
An early non-S Cayman could be a solution, but I’m sure there’s some porsche tax on the consumables. I want to say 944, but they need an engine swap to not be driving in the mirrors.
I think a 4th gen camaro might fit the criteria based on the one I had, but they aren’t terribly easy to work on. I’ve always preferred how the Camaro 3rd and 4th gen drive vs Mustangs of the same era, but ymmv.
350z (and maybe even a G35) could work as well. Good aftermarket, VQ is pretty well known by now.
You’ve already had a BRZ/FRS, but that would be on the list too.
These are all RWD cars. I personally consistently have more fun on the track in a RWD car. That’s just me. If you’re open to FWD, Civic SI would be high on my list. GTI breaks my turbo/reliability rule, along with the Focus and Fiesta ST. EP3 Civic or first gen TSX could be interesting, but they’re maybe too much of unicorns and maybe need more oomph.