I'm so glad you're having fun with this Geezer challenge and raising it to new art forms!
The Spa race is my new favorite, with its beginning in the rain, and the subsequently drying track. The rabbits are usually far faster than me in top speed, (once the track dries) which makes for some fun between Eau Rouge and Les Combes.
After Eau Rouge, I'm usually on the ragged edge and cut the left-hander at Raidillon hoping to miss the wall on the left. This excursion seems to give me an edge, so that when the following rabbit uses his long legs, he'll catch me but I outbrake him into Les Combes.
For the rest of the lap, rabbits keep close, but not close enough, and my final area of "rabbit threat" comes after Paul Frère, especially from Blanchimont through to the Chicane. I have refined late braking into the Chicane combined with hogging the line. The one time I opened the door, the rabbit rammed me, I got a penalty and he walked away with my money. I was not pleased, but it taught me a lesson about legitimately defending the line.
On my rig, with 720p TVs, approaching the Chicane I see a faint white line across the track. This I use as a braking point in most cars. Some cars with less braking power will not appreciate this lateness.
I enjoy this event's "rubber banding", because it seems to make sense.
The rabbit is slow on a wet track, but gains confidence as the track dries especially when he can see that a Geezer in an ancient American land yacht can negotiate the curves. At least that's how it is in my mind.
Final note. Spa was my "bête noir" until this seasonal. It scared the heck out of me, especially the Chicane and Eau Rouge. Being "forced" to do five laps at a time, and in the rain for the first of these has been a gift.