You are asking to open a can of worms. The 3800 is picky to rebuilds. Most people just get junkyard engines when theirs crap out. A lot of people who "rebuild" their engine end up with a 500 mile engine after the rebuild.
There is a guy on another forum who has around $3000 into his proper rebuild.
There is no need to remove the engine to do cam, lifters and springs. The spark plugs are easily doable without removing the engine. That's extreme overkill.
Another thing you have to worry about is the transmission on these cars. If you start modding and putting more power through it the transmission is bound to give up, especially with beating on the car racing it.
My honest opinion, these cars aren't fast. Even if you add cam, lifter, springs, headers, a pulley drop and a tune (yeah, you're going to need a tune to or you're bound to meet chip) you're still likely to get beat by current generation sedans such as Maximas and the like. That coupled with the weak transmissions and host of other GM issues makes them not worth going crazy with mods on.
All I have done to mine is a homemade intake and a 3" downpipe. The downpipe was only purchased out of necessity due to a hole in the flex on my stock pipe.
I'm not trying to pee in your cheerios here, just throwing out some real world advice to maybe save you some money and heartache.