While I'm in there, might as well... (Head Gasket Repair/Performance Upgrades)
 

Looks like I'm going to need a head gasket - white froth in the oil.

While I'm getting the engine rebuilt is there any upgrade that's worth doing?
I'd like to supercharge it one day so I'm thinking cold rings, forged pistons
Or should I just save my pennies for this: https://vancouver.craigslist.ca/van/ctd/5814496648.html

Thanks!

Save extra pennies to swap up those ugly wheels on the G37 if you go that route...

The options are fortifying the engine parts for a turbo or supercharger OR going with just cams, intake/exhaust plenum spacer

Your other option was saving up for the G37 you linked in the craigslist ad. That's what I was referring to.

If your current car is in otherwise good condition, already paid off and you don't mind spending a lot more than its worth then forced induction is the way to go.

I remember years ago I had a 1984 Nissan Sentra. When I bought it, it had 134,000 plus miles on it. Every time I talked-about modding it someone would say I'm spending more money than it's worth. I installed a Pacesetter header, K&N drop in air filter for the carburetor. Cross drilled rotors in the front (it had drums in the rear), upgraded the stereo, monza style muffler, tinted the windows, swapped the 13 inch rims for 15's with 195' in the front and 205's in the rear. It was a fun car to own and drive and it got a lot of attention. I latter traded it in for a 944 turbo. What I'm getting at is. It's your car, no matter what you do, somebody's going to say your spending more than it's worth. Their are guys buying twin turbo setups and new transmissions for their Lamborghinis and they too spend more than it's worth. It's your car build it however you want and enjoy the process. I just hope you don't rice it out but, if you do again, it's your car.

I did the same with a couple of Celicas. I'm just saying that are cars aren't worth very much these days (which is great if you bought yours used like I did) so you should be okay with spending money you'll never get back. Some people are fine with that, other's aren't.