Yes you do need to be invited, and we dont get one, not sure when we last did, I know PB did it but he may have been invited as part of his other successes.
It has been suggested to me that as a rule of thumb, you need 50 entries at your nationals to be invited, note thats as a rule of thumb, not a rule as clearly there are classes there that dont fit that bill.
I contemplated a bit of light lobbying this year, but didnt get round to it, I doubt it would have made much difference as with a finite number of boats available presumably its a one out one in arrangement, I have mixed feelings about its usefulness to the class, if you win great, if you dont - not so great and given the difference between a xenon and a cherub I'd hazard we'd be nearer the latter which may add some fuel to certain fires....