I have the 1.5 cvt and I average 44-45 mpg at 70 mph. I drive about 90% highway. City drops my mileage a lot. I did a few tanks with 50/50 city/highway and I averaged about 32-33 mpg.
Engines are constantly evolving and the Si engine should be capable of holding around 300tq+ stock internals. So yes a turbo upgrade would be fine for longevity.
The stock turbo is nothing special, it spools quick but that's about it. There are turbos that can spool almost as quick, but make...
Longevity of the turbo maybe, the engine itself will be fine. These tiny turbos usually max out around 25-26 psi before you start the shorten their life significantly.
Settings -> System -> scroll all the way down and touch Factory Data Reset and touch "YES" or "OK" about 4 times and don't turn your car off until the system comes back on.
You hurt you're engine more by changing the engine oil more often. When you first start the engine after changing the oil, it takes a little bit to circulate the entire engine and build pressure. This causes damage.
I'm not saying you can't change it before it needs to be changed. I'm saying that you can't judge any lubricating fluid based on it's appearance (unless it's milky or very thin/thick). Many lubricating fluids will turn brown or black within a few thousand miles. This is by design.
The color is not an indicator.
If you really want to know you should send two samples to Blackstone labs. A clean baseline and a used sample. They will analyze it and then tell you whether the used sample is still good and estimate how much longer it will perform.
The maintenance minder doesn't recommend CVT fluid change until 50k miles or more. It is based on driving conditions and loads.
Even the dealer recommends 60k miles.