Easy Call Down or Tough Fold (or Press an Advantage)?

[Catt]

UTG was decent post-flop, but too aggro pre-flop, especially if the table dropped to 5- or 4-handed (as it was here). Feel free to comment on pre-flop, but I'm pretty comfortable with my 3-bet in this situation.

Villain in this hand is crabway. I have limited stats on him at 22/16/1.8/45 over ~300 hands. He seems (at least lately) to regularly play the 30/60 6-max tables and 50/100 6-max tables (I don't have any insight as to whether he plays any 100/200). I don't have a great read on his play, but if I were forced to give a better read (and I generally force myself to give at least some weight to thin reads) I'd say he's a bit too passive and a bit too tight. My image should be reasonably solid -- I'm playing reasonably well, I'm up a fair bit, I'm showing down winners, and I haven't (to my memory) been caught in some ridiculous three-barrel bluff or supremely thin calldowns.

Party Poker 30/60 Hold'em (4 handed) converter

Preflop: Hero is SB with A[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/diamond.gif[/img].
<font color="#CC3333">UTG raises</font>, <font color="#666666">1 fold</font>, <font color="#CC3333">Hero 3-bets</font>, BB calls, UTG calls.

Flop: (9 SB) A[img]/images/graemlins/spade.gif[/img], 5[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">Hero bets</font>, BB calls, UTG calls.

Turn: (6 BB) 4[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">Hero bets</font>, <font color="#CC3333">BB raises</font>, UTG folds, Hero calls.

River: (10 BB) A[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">BB bets</font>, Hero calls.

Final Pot: 12 BB

Is there a reasonable argument for folding anywhere? Is there a reasonable argument (put aside any metagame arguments) for showing more aggression on the turn or river? And, so "aggression" isn't misconstrued, is there any merit to leading the river? I was a bit torn in the hand and still a bit torn in reivewing the hand.