Is there anything you ever really wanted to fly? A box you never ticked. I don't know what your budget is but if you are looking to mark 25 years maybe splash out on an aircraft you always loved.
Maybe the vampire?
The spitfire?
Something ridiculous?
Something obscene?
Something perversely ordinary that only you understand
If you want to mark the day, do it properly. If you want to say goodbye and thanks to aviation, do it with a bang. Fly the bird you always coveted. There must be one you never got your hands on, or have to fly one last time.
You may find it was just the kick in the pants you needed to remind you why you took that first solo.