Very surprising reraise at the river

[Atropos]

Party Poker 0.50/1 Hold'em (10 handed)

Preflop: Hero is MP3 with 9[img]/images/graemlins/spade.gif[/img], A[img]/images/graemlins/spade.gif[/img]. MP2 posts a blind of $0.50.
UTG calls, UTG+1 folds, UTG+2 calls, MP1 folds, MP2 (poster) checks, Hero calls, CO folds, Button folds, SB completes, BB checks.

Flop: (6 SB) 8[img]/images/graemlins/diamond.gif[/img], J[img]/images/graemlins/spade.gif[/img], A[img]/images/graemlins/heart.gif[/img] <font color="blue">(6 players)</font>
SB checks, BB checks, UTG checks, UTG+2 checks, MP2 checks, <font color="CC3333">Hero bets</font>, SB folds, BB calls, UTG calls, UTG+2 folds, MP2 folds.

Turn: (4.50 BB) 5[img]/images/graemlins/diamond.gif[/img] <font color="blue">(3 players)</font>
BB checks, UTG checks, <font color="CC3333">Hero bets</font>, BB folds, UTG calls.

River: (6.50 BB) 7[img]/images/graemlins/heart.gif[/img] <font color="blue">(2 players)</font>
UTG checks, <font color="CC3333">Hero bets</font>, <font color="CC3333">UTG raises</font>, Hero calls.

Final Pot: 10.50 BB

The pot seems big enough that I usually have to call this down. But I also noticed that if these usual party fishes suddenly reraise me, they nearly always have hit two pair//trips at the river, but well I said nearly always.
So should I call this down? Had no valuable read on UTG, only knew he played somewhat bad, but not as bad as the typical party fish. I ruled out that he could have got a straight, the only possibility would be Trips or two pair or Ace with better kicker, or Ace with worse kicker. Should I call this down?