Do anti-collision lights in aircraft lose intensity over time?
No, however the intensity is a feature of the bulb rather than the purpose.

Historically, incandescent bulbs were used, followed by Xenon flashtubes. Currently, LEDs are used in anti-collision lights and other lights on aircraft.

Please note that there are some requirements needed for bulbs used. They are mentioned in 14 CFR 25.1399:


  Show a white light for at least 2 nautical miles at night under clear
  atmospheric conditions.