Automobile safety has come a long way in the 47 years since the early Zs appeared. When I got mine in 1971 there were no Mom Vans, SUVs, Hummers, F150 pick ups, or other daily driver land barges. I only had to avoid semi trucks on the freeway and delivery trucks in town to stand a chance in an accident. Easy.
Now, a Z is considered to be a fairly small lightweight car that won't do well in an accident, unless it hits another Z. Your Miata without airbags is in the same boat. An acquaintance and his Miata were in an accident with a truck and the truck ended up on the Miata driver's lap. He never thought about buying another small car.
By the time you buy a nice Z and upgrade and modify it the way you described, you'll be very close to the same money that would buy a fun to drive, relatively safe, FRS/BRZ. It's one of those "pay your money and take your chances" choices. My daily driver is a 4 wheel drive truck and my '71 240Z, '70 Porsche 914-6, and '63 Studebaker Avanti are for occasional use.
Dennis