What is Ra6? A dubious move or a brilliant idea?

I find it to be a very interesting and strong Budapest type Rook maneouver

Yes, but in what canna positions its good? Like my friend and opponent knew this is good as he has studied this stuff, but how can anyone else figure out?

the main thing is that white should have castled, and there shouldn't be easy control of g6/h6 squares for white...

White was me, sad lyf

I played in a daily Budapest Gambit tournament, and won most of my games from the white side with this:

h3 in the game was a wasted tempo. Black will take on e5 anyways after playing a5.

Ra6 is a common idea. Neither brilliant nor dubious

Ra6 is a nice idea and a good attacking pattern to keep in mind. The rook finds itself very far from the action with the bishop and queen still in the way before it can reach an active file, so it activates itself with a lift to a6 to get into the game faster.

By the way, in the Budapest as white it is recommended that you start with 4.Bf4 instead of 4.Nf3. As you can see in the game your bishop was trapped behind your pawns when you were forced to play 5. e3, get the bishop out first, defending the pawn at the same time, and you'll be good to go.

Hope this helps

and why is it just a plain board

hello

In opposite side castling: pawn storming is a common attacking idea.

In same side castling: rook lifts are a common attacking idea.

Here, you both castled kingside, so pawn storming isn't really feasible, as it will expose your own king. But lifting a rook up to the 3rd rank and coordinating it with a queen+bishop is quite thematic.

I've seen these ideas in other structures, it's very nice. 

yes - in general, you want to attack with pieces, not pawns. pawn storms (generally) are only a means to open up files for pieces.