Sounds like you want to do it, so what we tell you doesn't matter.
Back in the day, it was something for a car to do 100,000m. Keep in mind most people don't do regular maintenance.
Now it's something for a car to do 300,000m+. Guess what? Most people still don't do proper regular maintenance.
IMHO I don't see why any car, with someone doing more than basic maintenance, staying pro-active in that car, AND keeping the open mind that "Hey... Normal shit breaks at some point!" shouldn't be able to put more than a million miles on most things Toyota has built in the last 15-20 years.
If you're going to keep the car a while, I don't see any reason to stop you. Just do a little more maintenance than required to keep it running.
If you're going to do some major power adder (n2o, turbo, s/c) I would *highly* suggest using seafoam to clean your intake track, fuel system, and oil crankcase (search the forum for seafoam). And find a hole on your intake (or take your airbox off and hole the throttle open some) and squirt 8-16oz of water with a water bottle into the intake. (squirt fast enough so slow the RPM down some, then back off just a hair. That's how fast you want to squirt the water in)
That will clean all the carbon out of your cumbustion chambers.
(my v6 when torn it down at 96,000 miles)
Don't mind the spilled oil/antifreeze scare you. Let the black carbon scare you.