Briers lack of international caps just reflects the fact the coaches made bad selection decisions and ignored a player with creativity and flair. I don't even think it was because he played for the 'wrong club' either...Tommy Martyn was in the same boat and played for Saints and got overlooked, another bad decision.
The thing I don't get with these stories about Briers, is people talk about him like he's some Paul Gascoigne type player, who drinks too much beer and doesn't look after his body and take his career seriously etc. Players like that are usually done by the time they are in their late 20s, they are a shadow of the player they were. But with Briers it's been the opposite, he was a player with ability that lacked consistency in his early 20s but from about the age of 27 onwards he's been pretty consistent and since he turned 30 (admittedly coinciding with the time Warrington have put better players around him), he's played the best rugby of his career.
Compare him to his peers ie the generation of halfbacks that came through around his time - Richard Horne, Paul Cooke, Chris Thorman, Danny Orr, these guys were all regarded at one point as ahead of Briers for consistency or attitude or whatever but all of them had dipped a lot by the time they hit their late 20s, they were not the players they had promised to be. Even Iestyn Harris, who I would have put as streets ahead of Briers in his early days, became pedestrian by the time he'd returned from union aged about 28 or so...compare the Harris of his later years with Briers at the same age and Briers is about ten leagues ahead of him.
There will always be people on the internet with their anecdotes about Briers with his beer and pies being a bad professional but his fitness has never been an issue and his on field performances have steadily improved through his career which is why he's enjoyed winning some trophies towards the end of his career which most people thought he would never get. So I think the truth about Briers is less exciting than the internet stories suggest...he's actually a top professional at the top of his sport. I know that secretly you Saints fans respect him and wish he had stayed at his home town club...you would certainly have won some of those last five Grand Finals if you had him in your side.