I have a miata and have done a whole 1 race while the car has done 3. Miatas are kinda the "easy way" to do it- they're reliable as hell, a super capable platform, and you can use them in many different other ways successfully (ie Autox etc). I'd argue a non turbo'd or engine swapped miata will not win a Lemons race unless by attrition or a super organized team because they lack straight line speed. That being said- my largely stock suspensioned miata out brakes and corners the vast majority of the field which can make driving quickly challenging but fun. It is frustrating to be passed uphill by cars consistently tho. If you want to be competitive overall I'd either somehow add significant power (turbo/engine swap) and get organized. What I'd recommend overall tho is run what you got, enjoy the whole thing and experience, fuel in your paddock slot, and try to not crash. Get Pagel involved early in cage build/design because you want one that will go above the normal miata roofline- mine doesn't and even with a drop floor pan (a huge pain in the ass to do) I barely get under the cage with a helmet at 6'.
I'm a guy allowed one car by the wife and $ limitations, I have no 'shop' to work in, limited storage, I am not in the auto industry, and can't weld. A reliable and cheap car to tear around the track with a couple times a year is what the miata does for me and I also go to local autox and am hoping to do some hillclimbs and maybe ever rallyx with it. If I could go full gonzo and bring a ridiculous car powered by a remarkable engine I would- but the reality is my limitations of talent/workspace/time keep me from doing it. My overnight at the race involved replacing front brake pads and topping off the oil- but I can tell you if it wasn't for COVID limitations I'd have found a team doing major work and volunteered to help. I also cheer on the teams with the funky cars because they 'get it' in a way I just can't do.
In summary- bring something that'll go around the track fast enough it isn't a hazard, bring something you can actually drive decently (don't be a '24 seconds of Lemons' type), MAKE IT SAFE, and enjoy the experience. If you're here to !RACE! on your first time around- you're not getting it IMHO.
If you message me I can tell you what cheap/free mods I have done to my 1.8 that have made me slower than many "B" class cars!
El Capitan of Team Corky
94 Miata covered in cork as Mazda/Toyo Kogyo tribute