Overpair boat with tripped board - value bet?

[Piece of Cake]

No reads. I've obviously induced this checkraise so I have to snap call correct? Was my river value bet wrong? Am I wrong to bet smallish the whole way to get underpairs to hang around?

PokerStars No-Limit Hold'em, $0.50 BB (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Hero ($77.55)
SB ($49.50)
BB ($16.80)
UTG ($29.50)
MP ($79.90)
CO ($49)

Preflop: Hero is Button with J[img]/images/graemlins/spade.gif[/img], J[img]/images/graemlins/diamond.gif[/img].
UTG calls $0.50, <font color="#666666">2 folds</font>, <font color="#CC3333">Hero raises to $2</font>, <font color="#666666">2 folds</font>, UTG calls $1.50.

Flop: ($4.75) 5[img]/images/graemlins/diamond.gif[/img], 5[img]/images/graemlins/club.gif[/img], 5[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
UTG checks, <font color="#CC3333">Hero bets $3</font>, UTG calls $3.

Turn: ($10.75) 9[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
UTG checks, <font color="#CC3333">Hero bets $4</font>, UTG calls $4.

River: ($18.75) 2[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
UTG checks, <font color="#CC3333">Hero bets $6</font>, <font color="#CC3333">UTG raises to $20.5</font>, Hero ????