There is a hump in the exhaust, a buddy of mine has one and he mentioned getting that piece of the exhaust redone with a straight pipe. That is supposed to help some as well as the other mods you mentioned.
That is called the U-bend and you replace it with what they all the unbend delete.
I have a ZZP 3 inch shorty downpipe and a U-bend delete from a set of headers I installed on a 3800SC Fiero. Those two items will help alot on getting the exhaust side opened up on the car. I will sell both for $75 if you are interested in them. You could take the 2 items and either get a high flow CAT added in the middle or just a str* pipe.
Also you need to add a CAI to the car to open up the intake side. You can make this easly out of sewer pipe/connector that you buy from Home Dept.
You can drop to a 3.4 pulley and gain alot but will need to have a basic tune done along with dropping a heat range colder on the plugs(AL 104s).
Also the M90 love the spray so of course that is a route you can take but with cautions of course.
These are pretty simple MODs that don't cost alot but give pretty good gains on the car. If you plan to start adding MODs then you need to invest in a scanner to monitor the car while running it. Of course like mentioned the trans is the weak point but you have a ways to go before worring alot about it.
My DD is a modded ICed 3800SC Fiero so I can help you out on things if needed on the car. I have also done 6 or so other swaps into Fieros using the 3800SC.