Before I went turbo, I didn't realise how hard it was to tune NA. If I was going back to NA again, it would have to be a big lump or something with VTEC.
As above though, exhuast and air filter are really yhe only way to go, might improve resposiveness a little and maybe a smidge of torque but they'll mainly just add noise. If you're serious about tuning it, stiffen the suspension and strip it out.