Semi bluff turn/ River Bluff - +EV or burning chips?

[DpR]

I think I should have bet out on the flop here, but given that I didnt I try the semi bluff on the turn with the scare card, unforuntley get called so I try again on the river. Is this too expensive a play to be +EV ? It has worked of course, but not sure if it works enough....

Party Poker 5/10 Hold'em (10 handed)

Preflop: Hero is MP1 with K[img]/images/graemlins/club.gif[/img], T[img]/images/graemlins/club.gif[/img].
<font color="666666">2 folds</font>, UTG+2 calls, <font color="CC3333">Hero raises</font>, <font color="666666">3 folds</font>, Button calls, <font color="666666">1 fold</font>, BB calls, UTG+2 calls.

Flop: (8.40 SB) 2[img]/images/graemlins/spade.gif[/img], Q[img]/images/graemlins/diamond.gif[/img], 9[img]/images/graemlins/diamond.gif[/img] <font color="blue">(4 players)</font>
BB checks, UTG+2 checks, Hero checks, <font color="CC3333">Button bets</font>, BB folds, UTG+2 folds, Hero calls.

Turn: (5.20 BB) A[img]/images/graemlins/heart.gif[/img] <font color="blue">(2 players)</font>
Hero checks, <font color="CC3333">Button bets</font>, <font color="CC3333">Hero raises</font>, Button calls.

River: (9.20 BB) 8[img]/images/graemlins/heart.gif[/img] <font color="blue">(2 players)</font>
<font color="CC3333">Hero bets[/color

Final Pot: 11.20 BB
<font color="green">Main Pot: 11.20 BB, between Hero and Button.</font>