Thank you, vallescure!
I already spotted this game in ICCF games database, but didn't know it was you with black.
Right now I play a game in this variation, but I chose 12.c3 instead of Gavrilakis' 12.Nf4... (just to try something new in order to have chances for a win). These black's knight dances on d4, back to c6 and a5 seem strange (maybe this is the reason that Vigorito and Cornette never looked at this continuation), but are somehow tangible and white has to be very careful.
Anyway, the problem is that black can transpose to this position by playing 4...e6 and 5...Nf6 first and then 6...a6 (instead of 4...a6 at once) as it was in my game. So, 5.Nce2 for white wouldn't be available then.
As for your game, I respect your decision not to play 12...Bb7 or 13...Bb7, thus letting 15...Rb8 to support your b-pawn with a rook in order to attack the white c3 pawn. However, my opponent went for Bb7 (on the 13-th move) delaying the black castle and took my bishop on b3 (after c2-c3) which gave him a good game, too.. It's still running, that's why I shall refrain from giving all the details here. 

There is a book called Experts on the Anti-Sicilian (2011) edited by Jacob Aagaard & John Shaw. GM Matthieu Cornette of France wrote some excellent chapters upon the so-called Modern (Tiviakov) Grand Prix which could have been a reasonably sized book on their own.
On page 337 he gave his options against 4...a6. In brief, he stated in the above-mentioned book that 5.d3 is his preferred move in this exact position, as well as he cited many transpositions after 5.a4 (leading to another line) and 5.Nge2 which can be met by 5...b5!? (instead of 5...Nf6 which transposes to the so-called main line). 5.Nf3 b5!? was  reviewed, too..
The move 5.Bb3 was not considered (maybe that's why your opponent played it, after all), but can lead to another transposition, of course.
Imho, this "Modern" Grand Prix is very interesting, as well as not heavy on theory. So, that's why it drew the attention of so many correspondence and OTB players. Hence, the strategy! 
Anyway, black has several continuations (including 4...a6) which are very good and give the second player a good game. White strategy here is the usual Grand Prix's strategy. Keep the white bishop alive if you can and start an attack on the black king after f2-f4 and so on. If not 3...Nd4 (which is the best continuation, imho), then the first player destroys the black pawns structure with Bxc6 before black can play Nge7 or Bd7, then plays f2-f4, d2-d3, Bc1-d2 and Qd1-e1-h4 with a possible attack on the kingside or Nc3-a4, b2-b3, c2-c4, Bc1-a3, Ra1-c1 to attack the black pawn on c5, all depending of black's continuations.
Nothing new under the sun.. 
Just to add that now I play this opening with white in my correspondence chess tries for the third time. One exciting victory for now, another one is cooking (I hope), while the third one...hmmm, black (a big name in the correspondence chess) played very, very interesting.. Even GM Cornette haven't considered such continuation. And I cannot say I have a good game, for now.. 

Maybe white can play 5.d3 and transport to other lines with Nge2/Nf3 that he will play at next move.
Any opinions?
Does vigorito include this move?

I played Vigorito's suggested 4...a6, not really knowing this variation. The first 10 moves ended with the same position as that in the e-book line.
I managed to draw with my 200+ graded opponent so have to say it went quite well for me.

1.e4 c5 2.Nc3 Nc6 3.Bb5 Nd4 4.Bc4 a6 5.Nge2 b5 6.Bd5 Rb8 7.Nxd4 cxd4 8.Ne2 Nf6 9.Bb3 Nxe4 10.Nxd4 e6 so far, same position as ChessPub e-book, but with different moves. Maybe there are some improvements already?I felt Black was comfortable but went a bit wrong over the next few moves.
11.0-0 Bd6 12.Qe2 Bb7 13.d3 Nc5 14.Nf5 Qc7 15.Nxd6 Qxd6 16.Qg4 Nxb3 17.Bf4 and with 17...Qd4 I think I'm just holding on.

Anyways, thanks to ChessPub (Vigorito) for the 4..a6 suggestion!I think I would likely have been in a mess if I hadn't checked this before the game.

Please, anyone see any improvements in opening? (I'm likely to play the same opponent again next season - if not sooner).

Cheers, Tickly.