If I had to spend 8K I would make my car as reliable as possible first before I went throwing a bunch of power to it. Thats why so many people (not all) have their cars down for a while since they don't do required maintenance or forget to sure up their 15 year old drivetrain.
Since you already said you don't want huge power and talked about getting 13g's I wouldn't go through the hassle of getting a built motor. I would just make sure 60k/120k or whatever mileage you are at is done and get some oil analysis done to see if you need to replace your rod/main bearings.
Then I would take off your transfer case and check the condition of splines and input spool. If they are rusted to hell then I would replace with a 300mm output shaft and if your t-case spool looks rusted to hell then I would either rebuild it or get a SS t-case for peace of mind.
How's your syncros? If you grind into every shift I replace them and while the tranny is apart you may as well replace the output shaft. Also you should get rid of any backlash in you drivetrain like at the rear diff and also make sure your vcu is working.
It's hard to tell how much this would set you back since it would depend if you can do your own work or if you send it out.
With whatever you have left I would get:
-13t's (cheaper than 15g's and seem to be very close power-wise) ~1000
-datalogger ~100
-some real quality gauges including but not limited to oil pressure, boost, wideband, egt ~ 400+
-upgraded clutch ~ 600
-IPS Fuel package - 760
-boost controller - 300
- solid motor mounts (poly are for babies
)
-lightweight rims and tires + lowering springs + adjustable control arms ~2000
You could get all this for around $5000 depending if you find some deals in the parts for sale. The other $3000 should cover anything needed for 60K/120K and whatever you need to fix from the flywheel to the rear diff.
Mike