Is there any refutation to the Sicilian Grand Prix Attack?

Also, the early ...a6 plan is flexible in that black can always go for the typical K-side fianchetto if he feels that white's aggressive intentions can be countered adequately. 

I occasionally castle long as black but by and large I prefer to castle kingside and open the queenside to use it as a pivot to attack white's kingside. Occasionally I castle kingside and advance the g and f pawns, if the K is safe enough on h8. Sometimes black's K is safe in the centre, especially if pawns are still on f7, e6 and d7 or d6.

I don't really agree with your assessment, insofar as it fits (or doesn't fit!) what people actually play.

I've started playing 2. ... a6 against 2. Nc3 but I've been playing it against 2. Nf3 for at least 25 years. I'm starting to get good at it and have developed theory quite a bit.

Normally, the move order would be 1. e4 ... c5 2. Nc3 ...a6 3. f4, if white is determined to play the GPA. If black continues with b5, white can pressurise it with a4 and play to disrupt black's development. It can become quite a melee. However, I prefer a more principled development as black and would therefore play 3. ... e6, intending ... d5. White can no longer play the positional line with Bb5. This Bb5 started to appear more often 20 years ago in club and tournament circuits in the UK and I decided early on that it's strong for white in the hands of a strongly positional player. So I avoid it.

So white's development against 2. ...a6 with 3. g3 is actually a complete change of plan, where white makes the correctly principled decision that g3 is the best way forward, against an a6 Sicilian. It's no longer a GPA, although white may try to play f4 before Nf3.

I really like your position after 14. ...f5. Black is decidedly better. White immediately blunders, because he has to play 18. Qd2 and centralise rooks if possible. Bd2 is really bad.

@Optimissed I've given the lines with a4 as well as ...e6 and a quick ...d5 in the notes to the game above. I've also given black's plan against and early f4 by white (the key GPA move) in post #20.

Of course, I'm not a Polugaevsky or Zaitsev, so my opening suggestions need not be the best ever, but this particular line (at least to me) seems effective enough, especially on a psychological level.

I didn't notice anything much in post #20. You just said that you recommend ...b5. The idea with an early ... b5 is the method used by Kan. If white knows what he's doing, he will switch plans and attack the Q-side, when the only benefit of what black has played is really its surprise value. Black's Q-side is rather weak but it may be helped by the fact that white has played Nc3, which can be a tempo-target.

Tbh I don't think white has to change plans. White can play a4 and Bc4. Black's plan with e6 and Ne7 equalises and it's something that I've played. White can prepare for it with d3 and just drop back to Bb3. I would think the position is equal but black still has to be very careful. White's development is better than black's. Playing pawn on, d5-d4 can weaken black's position and that may be better avoided. When you come up against someone with white who deliberately plays for these positions, which isn't often, it can be a learning experience.

I like the early a6 plan, but there is a major weakness that you allow if white is not a hardcore closed sicilian player.

Now there is a weird open sicilian that scores quite well for white. The only drawback for white is that he has to resort to a true closed sicilian, since there wont be a grand prix attack with the knight on e2. So I guess it works as an anti-grand prix.

If black is playing a6 he probably plays some a6-based open sicilian he'll transpose into. Although that a6/b5 line still looks objectively on par with most other sicilians.

If I were a closed sicilian player I'd only play the grand prix vs. 2... d6.

2... a6 line is good, I've played around with it, but ultimately decided it didn't have the bite against g3 systems that 2... e6 has. It's still fine, you get opposing bishops and black has basically equalized, but I love the Korchnoi defense for black... it's very aggressive.

I sometimes play c5, a6, e6, d5 and if e4 then moves like g6, Be7, h5 and so on. It can be quite enjoyable.

If I remember right, this is an old line which black is ok in. Might have missed out a couple of moves though. Can't remember it clearly.

This is true, but I dont think this is the theory position that you are referring to.

Here is the "Main-Line" after 2... d6

Thanks, I think I faced it once or twice in the dim and distant past. Now I usually play either what I mentioned in #29 or just more simple plans based on e6 and d5. In the former, I prefer an early a6, or white can use one of those B b5 and swap off plans, with a very slight but long lasting positional advantage.

Whenever I face the sicilian, I usually play the closed sicilian. And I think the "Kan" setup against the closed sicilian is the most difficult system to face. So I think you have a good plan

Yes, against the closed, the idea is to try to bottle white up by expanding in the centre and on the Q-side. Then to try to take advatage of better communications by attacking on the k-side.

Smith-Morra Gambit clears the Sicilian.

With best play for black, white might just be able to get a draw. Therefore it's ok. A good try for a win maybe below 1900 FIDE. I'm a little stronger than that.

Smith-Morra is quite bad IMO. White isn't getting as much initiative as the players usually think they are - it takes tempo to play c3, what you're essentially doing is clearing the c pawn... but usually black winds up using that file, not white. And when black plays a6 > b5... which he wants to do anyway, the c2 diagonal isn't useful for the queen either. You also can't castle queenside... you're just down a pawn with little to show for it.
There are a few small, subtle advantages white gets, like making room for Bc2 later on. But Black can also play it slow, since... even if he never manages d5, he's just up a pawn anyway, there is no losing endgame as a consequence. I usually play e6 and keep my pawn on d7. 
It's not even that rare - it's a 2nd move line and one of the more common ones. It's honestly one of the easiest lines to deal with in the sicilian.

I do like the Morphy gambit transposition but people don't play that.

I mean I got a higher rating than you using this "inferior" response to the Silician so I must be doing something right crazedrat.

Here's a perfect example of the types of attack I can get with the Smith-Morra Gambit with 3.c3 after 2...exd4:

I always get many attacking chances, no matter what black players are after 2.d4. It give me a high win rate against the Silician and I always have the chance to get games like these.