I used to autocross a Honda Civic. Based on my track experience, when it comes to springs anything over an inch is for looks only, as it will have a detrimental effect on handling over typical road surfaces.
If you want the look of a lowered car and don't mind a mild downgrade in ride and ground clearance, do springs only. Go for the least amount of drop possible. A 1" drop (like the Nismo kit springs) is nearly indistinguishable from 1.5" looks-wise, and the car will handle broken roads and speed bumps better.
If you just want the biggest handling improvement at the lowest cost, do sport shocks and a rear sway bar first, then springs if your budget allows.
One of the nicest low-cost improvements I got when tuning my Honda, was alignment changes. A race shop should be able to dial in extra caster, which will give you quicker turn-in, stronger centering force and better feedback.
Strut and subframe bars help maintain alignment if you do a lot of hard driving. They also improve turn-in very slightly. These parts shouldn't be necessary for normal, mildly sporting street driving, and I would leave them for last.
If you're getting into autocross, harder steering rack and engine mounts will stiffen the front end as well, if they're available for the Versa. The motor mounts are not good for a commuter, as they transfer a lot of noise and vibration into the passenger compartment. I did hard Mugen mounts on my Honda, and they made it sound like an old K-car with a bad muffler...
If it were my money and my Versa, I would go with the Nismo kit. It's priced comparably to a set of Eibach springs and Tokico shocks, and the ride height and tuning will be as good or better.
My second choice for springs would be the taller set of Eibachs (Pro Kit). Eibachs generally give a decent handling improvement, without ruining the ride. I would not buy the orange springs shown earlier in this thread. 3 dead coils and only 2 active ones, is not indicative of a good performance spring design.