Who built your motor?!

As for what is worthwhile or not, depending on how much value you put into what aspects. Some might think that shooting $20K worth of paint on a car is worthwhile, some think pumping $10-$15 into an engine is worthwhile, up to the person.

Getting almost 9K-10K RPMS and boosting over 12PSI out of a 1ZZ-FE is pretty wild, with a modest budget - I'd say darn near impossible (need to post up some pics - or I call BS on this), and definitely not last too long. Unless the motor was built to hell and back, even then - those revs are pretty tough to obtain with the long stroke design of the 1ZZ-FE engine (91.5mm stroke/79mm bore). 7K RPMs I've seen, 8K RPMs is possible - but now you got enough money invested into it that you're pretty much committed to the project (i.e., designed/built the motor up to be oversquare to reduced the reciprocated mass to get up to those RPMs.)

If you started with a 2ZZ-GE - then I could see those revs, as that engine was designed from the start to be high revving (85mm stroke/82mm bore, special block design, cooling, lubrication, etc). Stock, they redline at 8200-8300 RPMs, and can run up to 9K RPMs on stock springs. With 25%-33% heavier - 10K RPMs is possible, but you will see excessive valvetrain wear and tear. There are development 2ZZ-GE that have spun up to 12K RPMS, heavily modified though.

Air-to-water intercooling is an interesting choice - could you enlighten us on that choice - was it yours or the tuner? Moding the fuel system to a return type from the OEM returnless is also widely done - depends on the tuner's backgroud. Power FC is a great choice of engine managment - good band for the buck there, but tuning will depend on the tuner's familiarity with the EMS system. Some tend to favor one or two manufacturers - since they have a library of maps that they pull from to set the baseline and go from.

Not sure why they are running cams, remove the VVT-i system (Power FC can control VVT-i) and then ultimately pull timing overall (unless I read your post incorrectly), especially if you running race fuel. Any details on the cams? Duration, lift, etc.?

Anyway - as far as the behavior of richening up at high RPMs - you'll have to ask the tuner of the engine. My first impression is that they purposely set the fuel map to enrich the mix as you are approaching redline to protect the engine from blowing up. Running a little rich will pull down combustion chamber temps and save the valves from getting burnt. Doesn't make the best power - but does save you from rebuilding the engine. When the engine is a not loaded down or run lightly - the fuel mix can approach stoichiometric or even run little lean to give you some efficiency.

No worries! Anything is possible with enough money. Seriously, you could build a "1ZZ-FE" to rev to 10K RPMs, problem would be by the end, it would resemble nothing like a 1ZZ-FE engine and probably set you back about $30K-$40K. There are a few undersquare engines that can rev pretty high - Audi (V8 and V10 engines) and Lamborgini (V8 and V10) are good examples.