Here's my 2c though I don't know how much help I'll be with 5 cars sitting in the driveway and only 3 drivers in the house - bottom line, if all you're going to do is 3-4 track events a year, I cannot imagine the "extra" car makes sense - especially when you start figuring ALL of the other costs involved.
When I say ALL I mean everything - insurance on the car if you still drive it on the street, insurance on the trailer/tow vehicle if you don't, maintenance on all of the above, etc., BUT most importantly the opportunity cost.
I started down this insanity with an E36 M3 which I purchased with the intent to start in HPDE and build into a race car, and I did just that and eventually got my license and when W2W. I regret none of it, and did a ton of it myself, had the whole tow rig went from open to enclosed trailer, and the whole thing grew. Grew to the point that just getting myself out of the house and to the track was an exhausting and stressful ordeal, taking a lot of the fun out of racing and track days.
2 year ago I made a spreadsheet - I put ALL of my costs on it including my time - time prepping for a race weekend, time picking up the trailer from its storage location and dropping it off after the weekend, time loading/unloading, time wrenching on the all of the things that broke after weekend - and I gave myself a value of $50/hr for all of it. Then I compared what one of the local race shops wanted to do it all for me and you know what? I either break even or "make money" with them doing it and eliminate 99% of the headaches. I sold my truck and trailer, gave them the car, and I show up and drive - it has been one of the best decisions I've ever made (in the context of the stupid decision to spend all of my money going racing).
Here's the rub - there's an NB Miata now sitting in my driveway because I want to be at the track or doing something fun with a car at least once a month, I have a soon to be 16yo old son I want to bring into this insanity with some autocross and get him into track days, plus I want to go back to the "simplicity" of a track day without it costing me $$$ to have the team bring out the race car. I don't enjoy my daily driver Audi B8 S4 on the track, so I am trying desperately to create that dual purpose car that we can tool around town on the weekends, drive to/from the track, have fun with and bring home in one piece. The voices in my head tell me this all makes perfectly good sense, and I enjoy the tinkering, the lack of deadlines (if the car isn't "ready" it doesn't matter), building and prepping the car with my kid, etc. But I can also tell you I've already found my brain wandering to the hideaway hitch for the Miata, building a harbor freight tire/fuel/tool trailer to drag behind, and I know the rabbit hole is there waiting for me to drive down it.
I remind my wife that the whole thing is if not cheaper than hookers and blow, at least more socially acceptable, I get to hang out with my teenage kid and my dad at the racetrack, and having a toy at home to wrench on and play with gives me something to look forward to on the really stressful days at the office. Those are the "costs" that can't be calculated that are invaluable IMHO.