As near as I can tell, there's no option for a season.nfo, but that would be a great feature. Not just for sports, but for any show that spans multiple seasons, i.e. from The Wire
wiki entry, "The fourth season expanded its scope again to include an examination of the school system. Other major plots include the mayoral race that continues the political storyline begun in season three, and a closer look at Marlo Stanfield's drug gang, which has grown to control most of western Baltimore's trafficking."
One problem is that none of the common TV scraper sources I'm aware of support season-level descriptions, so that info would need to be added to thetvdb.com or whatever, or entered manually.
Regarding <episodeactorsource> I still have no idea what it's for, I noticed it in Hoobie7's tvshow.nfo file.
As far as organization goes, I would put a single tvshow.nfo in the F1 root folder, and just make it a generic plot which would apply to multiple seasons. Mine is from wikipedia, and tells a little about the history of F1. You can either leave the drivers out of tvshow.nfo or update them each year, but either way you should include the drivers in each episode nfo. Then in the first episode of each season you could do the plot you would have included in a season.nfo file. Talk a little about changes in the rules for the new season, etc. This is my plot for Australia, "After the cancellation of the Bahrain F1 GP the opening race of the 2011 FIA Formula One World Championship season takes place at the Albert Park GP Circuit in Melbourne for the QANTAS Australian F1 GP. Making an F1 debut is the 'adjustable rear wing' system in place of the banned double diffusers, adjustable front wings and f-ducts. During the race, drivers will only be able to use the system on a designated overtaking zone of the circuit, to be decided by the race director, when they are within one second of the car in front. The wing returns to its fixed position when drivers apply the brakes. The 'adjustable rear wing' system can be used anywhere anytime during practice and qualifying. The kinetic energy recovery system (KERS) also returns after being used by some teams in 2009. How they work together in improving overtaking opportunities is yet to be seen."
I'm going to do some research and either feature-request the addition of season.nfo or find out how difficult it would be to put the information somewhere and mod a skin to show it.
In other news, I'm working on episode thumbs using Hoobie7's great track maps provided in the OP. The layout isn't quite right as the image is being cropped weirdly for some reason, but once I finish them I'll post a link in case anyone wants them.