Teach me how to value bet please

[neff]

Been at the table for about 35 minutes. Villain is a very fishy 57/12. I'm not a gifted hand reader but this guy just makes it too easy. When he check raises, he has the nuts, and he only does this on the river. When he leads out, he has a draw of some kind. I stacked him with QJ on a Q953 two spade board, he lead out and called my push with A5s. I'm 98.5% certain he has a weak ace here, but with this guy a river check raise is always possible with a monster(even a hand like 10 4, I've seen it before). With this description how easy of a value bet is this? Any comments would be appreciated. On to the hand:

Full Tilt Poker
No Limit Holdem Ring game
Blinds: $1/$2
5 players
Converter

Stack sizes:
Hero: $412
CO: $195
Button: $275.70
SB: $200
BB: $291.25

Pre-flop: (5 players) Hero is UTG with A[img]/images/graemlins/heart.gif[/img] 8[img]/images/graemlins/heart.gif[/img]
<font color="#cc0000">Hero raises to $7</font>, CO folds, Button calls, SB folds, BB calls.

Flop: 2[img]/images/graemlins/heart.gif[/img] T[img]/images/graemlins/diamond.gif[/img] A[img]/images/graemlins/spade.gif[/img] ($22, 3 players)
BB checks, <font color="#cc0000">Hero bets $16</font>, Button calls, BB folds.

Turn: K[img]/images/graemlins/heart.gif[/img] ($54, 2 players)
<font color="#cc0000">Hero bets $38</font>, Button calls.

River: 4[img]/images/graemlins/diamond.gif[/img] ($130, 2 players)