Hello again

I have a 1990 740 GLE 16-valve and I am curious to find out a list of all posible performance upgrades that I can do to this car. I am aware of most of the suspesion related upgrades (i.e sway bars, spring, shocks/struts etc.), I am looking for more on the engine side. I am going to be putting in a K&N air filter this weekend if the local retailer has one in stock and I am planning on putting on an IPD performance exhaust in the near future (it is still a little cold and snowy out right now :-) ) Is there anything else available for me to do? or is that basically it? I have heard of some sort of insert that changes the flow of air supposedly giving you more power (unfortunately the name escapes me). Has anyone used these? do they work? pros and cons? this is the closest I could find http://www.spiralmax.com/sm_photo.htm
Your thoughts on this and any other information would be appreciated
Thanks in advance

Neil