Value bet on semi-dangerous board: too thin?

[DMoogle]

Villain is unknown, has been 33/11 over the past 27 hands. He tanked before checking the river. I like thin value bets, but is this too thin? What about my bet size?


Full Tilt Poker - No Limit Hold'em Cash Game - $3/$6 Blinds - 5 Players - (LegoPoker Hand History Converter)

SB: $700.00
BB: $415.90
Hero (UTG): $663.00
CO: $651.90
BTN: $916.70

Preflop: Hero is dealt 8[img]/images/graemlins/diamond.gif[/img] 8[img]/images/graemlins/spade.gif[/img] (5 Players)
<font color="red">Hero raises to $21.00</font>, 2 folds, SB calls $18.00, BB calls $15.00

Flop: ($63) 7[img]/images/graemlins/heart.gif[/img] 5[img]/images/graemlins/spade.gif[/img] 3[img]/images/graemlins/diamond.gif[/img] (3 Players)
SB checks, BB checks, <font color="red">Hero bets $45.00</font>, SB folds, BB calls $45.00

Turn: ($153) 7[img]/images/graemlins/heart.gif[/img] 5[img]/images/graemlins/spade.gif[/img] 3[img]/images/graemlins/diamond.gif[/img] K[img]/images/graemlins/diamond.gif[/img] (2 Players)
BB checks, Hero checks

River: ($153) 7[img]/images/graemlins/heart.gif[/img] 5[img]/images/graemlins/spade.gif[/img] 3[img]/images/graemlins/diamond.gif[/img] K[img]/images/graemlins/diamond.gif[/img] 5[img]/images/graemlins/club.gif[/img] (2 Players)
BB checks, <font color="red">Hero bets $75.00</font>