Take bhp figures with a pinch of salt on rroads, so many factors involved, just some are temperature on the day, what rollers, the operator etc Iwould be more than happy with that result and those mods.
Youre graph looks like most standard Z22SE's.
Like you say you need a new exhaust and plugs, standard ones are by far the best.
What other cars ran on the day? Did they make power the owners thought?
Has you car been on a rr'd before?
Put it this way my car with its old lump made 155 on one rr'd a month later with fresh service and sports cat and 4-1 manifold it lost about 25bhp, after the mods the car felt quicker so I really wouldn't worry at all.
One thing I would say, if it's a good rr'd and you like the place keep going back to it to check your power after mods are done that is if you want to see the increase on paper.
