Actually, Miatas are pretty good at crash survivability. Light weight can help there too (you bounce of some things that heavier cars would plow into).
I was worried about the power thing too when I switched from an RX-7 to my Miata but it hasn't been too big a deal. Nobody races you in a Miata and it's such a joy to drive that the only competition you'll care about much is yourself.
"Can I take this corner a bit faster than last time" or "Just 2 inches closer to the apex and I'll freakin rule!"
Not that it isn't underpowered, it certainly is, but the car is so much not about power it is forgivable... a bit. It can be disheartening to mash on the gas at the exit of a perfectly taken uphill corner and get very little. I am saving up for a cold-side supercharger after all.
Speaking of which, something to keep in mind is that there is virtually no way to add any significant power to the Miata for under $2,000. 1.6L cars can be turboed for 2 grand and 1.8s can be hot-side supercharged for the same, but CAIs, exhaust mods and such will just make the car sound better.