mariegrosjean wrote: Can I tell by the brake fluid level at all, or are there any other "warning" signs?
One way is by checking the color. If you're using a typical DOT 4 fluid and it's "tea" colored, it will tend to go dark to black over time and many heat cycles. If your reservoir is getting dark, you're due for a change. Keep in mind the "gunk" that collects in the brake fluid often falls downward to the calipers where you can't see it. So if the fluid is turning color in the reservoir, the fluid in your calipers may be .....

!
Time is your other enemy. The longer the time, the more degraded your fluid. Do you live near the beach or bay? Even more problematic. Once a year for a complete bleed is good. Twice a year is better.
If you notice your brake pedal going soft after a couple of laps of hard braking ... it's time.
I really like the ATE Blue and Ate Gold for intense driving events. I know Dealer Service departments tend to steer away from these fluid and that's why I recommend a service provider like Black Forest, Dieters, and Mirage. With your splash guards on the back of the rotors (that tend to trap heat) you're going to be giving your brake fluid a real work-out.
As a side note, I've had more than one service provider ask me who does my brakes ... "the firmness of the pedal is really impressive." The answer: "I do them myself." When it comes to brakes, I leave nothing to doubt ( and .... Anthony at Black Forest does one heck of a great job on caliper rebuilds

).
That's one driver's opinion. Others may vary.