NL$50 turning my hand into a bluff

My read is he's an ok player playing at 12/10/2 and always c-bets regardless of # of opponents (so slightly spewy). On the turn when he calls I'm sure I'm behind. On the river I'm nearly sure he doesn't have a spade that he'd c/c with. So I stayed with my read and fired the river, what say you?

PokerStars No-Limit Hold'em, $0.50 BB (7 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

MP2 ($30.95)
Hero ($55.60)
Button ($48.40)
SB ($50.20)
BB ($81.90)
UTG ($12.25)
MP1 ($50.75)

Preflop: Hero is CO with 6http://www.flopturnriver.com/phpBB2/...miles/club.gif, 8http://www.flopturnriver.com/phpBB2/...miles/club.gif.
1 fold, MP1 raises to $1.75, MP2 calls $1.75, Hero calls $1.75, 3 folds.

Flop: ($6) 8http://www.flopturnriver.com/phpBB2/...iles/spade.gif, 3http://www.flopturnriver.com/phpBB2/...iles/spade.gif, Khttp://www.flopturnriver.com/phpBB2/...miles/club.gif (3 players)
MP1 bets $3.5, MP2 folds, Hero calls $3.50.

Turn: ($13) 4http://www.flopturnriver.com/phpBB2/...iles/spade.gif (2 players)
MP1 checks, Hero bets $9, MP1 calls $9.

River: ($31) 2http://www.flopturnriver.com/phpBB2/...iles/spade.gif (2 players)
MP1 checks, Hero bets $20

meh, I think $12-15 does the same thing for ya. He could easily have Ks in his range though so bigger might be better.