both of those together may give you a very small increase. like .5psi. I doubt the smic will change it hardly at all.
Different plugs aren't necessary. I would look into a hi-flow or catless midpipe (most noticible power mod). Also I converted my Hiboost intake to CAI and it raised my boost by 1psi.
A fmic will raise the boost.
http://www.mazdas247.com/forum/showthread.php?t=123676839
Here is a GB on a FMIC kit, it is close to being over. Check it out and throw your name on the list if you're down.
Again, your boost will not increase with the stock exhaust. the car will be faster and happier though. Exhaust is easy to change. Intake is easy too -- just get a filter and replace the airbox with it. you don't even need different piping. after that you will see your boost increase.
well done. you'll be happy with that, especially once you free up the exhaust. After that you're probably safe to run 7-8psi if it doesn't get turned up to that already.