I feel kinda obligated to chime in here being a noob on the board with a Miata.
I've had 2 so far: A '90 (1.6), and a '95 (1.8). Both were stock when I got them, and both eventually had suspension & intake/exhaust work done on them. Statically, the '90 was probably slower than the '95 acceleration wise, but the free(er) revving nature of the 1.6 and the lighter weight made it feel more urgent. This was stock.
Now on the 1.6 I had custom fabed an intake using a K&N filter and had an Enthuza cat-back on. Those two mods added a bit of kick to it, but it didn't do much. In a drag type race I'd loose to just about anything on the street short of an Echo.
Now the 1.8 I have now with a MonsterFlow intake and Enthuza exhaust, plugs and timing bump, has some balls. The biggest improvement came with the intake. It helped noticeably in midrange torque to redline while also seriously improving the throttle response.
And while not exactly a fast car, you would hardly call it slow.
Just the other day I drove my friends stock MSP, and while it did pull a bit harder than my '95, it wasn't by much.
Now when it comes to back road barnstorming....good-bye. (burnout)