The F2 finals (now BRC's) have always been open to any license grade of F2 or below. It's just in the good ol' days virtually every F2 in the country wanted to race at them, so the lower license grades went on the reserve list.
I remember going to the F2 finals at Holbeach as an F3 (I think) and being reserve for the Mid-West. Luckily I did get a place.
As for what the F2 means, I'd say, if you're thinking of competing at Nationals the following year, that is probably the most important thing to aim for at Regionals. This will give you one of the best chances possible to get an entry.