Go have fun and be safe.
Many people said my Uno SX with less than 50BHP at the wheels was a non starter. How wrong they were. IT IS NOT the car it is the driver, the attention to mastering the bag of underpowered bones and experience that count. The whole objective of track days is about safely mastering the skills and having safe and enjoyable fun. This same objective is also present when one first starts to competivley sprint or even race. You are building a CRAFT which takes time, practice, time and practice again and again. Personally I have no time or patience for I've got xxx BHP, lower this, stiffer that, fatter that etc. etc. as 9 times out of 10 they can't deliver what SHOULD BE DELIVERED from their package.
The the point of Track Days is for people to safely access, drive and gain experience in what ever car they arrive in. Track days are NOT race days and the only competitor is yourself! Competing against yourself to slowly and safely improve and hone your skills and to bring yourself and the car safely back to the pits and back home time and time again.
Just about all knowledgeable experts will support that the driver who starts with a 1bhp, bad handling, bad braking, bad understeer etc. etc car will learn and understand masses of information and experience. When they progress to a better car that better car will fly faster and more accurately than many more experience drivers who never drove and learnt how to master the inferior car.
This skill and experience progress is what makes a) motor sport expensive and b) supports progression to the higher ranks.
So the concept of a "good track day car" is irrelevant.
However the concept/criteria of a good competition hill climb, sprinting, race or endurance race car is a completely different discussion.
If you want to enjoy a good track day then take whatever car you have, check it out for safety (tyres, pressures, brake pad thickness, secured engine, passenger, boot compartments and ideally unload everything other than you, your seat belt, self preservation etc. and certainly DO DUMP the ego, I'm as good driver, I'm a fast driver, I know what I'm doing etc. well before the pit lane. Do this and you will "Live Long And Prosper".