It's ok to attack on these boards every now and then just to keep your opponents guessing. At higher stakes this half-a-pot on paired board is more like mandatory but in micros especially more fishy players doesn't do it that much unless they actually have it. If you have good reads that your opponent is somewhat solid reg who probably knows this maneuver and is using it, then go ahead and raise it. If you don't have too much information about villain, just let it go.
This kind of board can be problematic in a sense that you shouldn't have that much of 5xxx or 22xx hands in your range, let alone 52xx. This combined with the fact that in micros even the regs doesn't like to fold too much, may force us to multistreet bluffing. With this small raise (which i think is just fine, or 0,65-0,7$) villain could think that he don't want to fold for example a nutFD/AAxx because of the odds (or whatever excuse they give themselves) so it's not very unusual that some of the players call that one bet.
That been said, either the villain shouldn't have that much 22xx/5xxx hands in his range when he's isolating on MP.
Ace kind of sucks because AAxx is in his range and for some people it's really difficult hand to fold. 
However, when you have one A, it naturally reduces AAxx combos. A5xx can easily be in our range so i think the turn is good card for us to barreling.
When he calls that also, and he is somewhat solidish reg i would be really worried about him having AAxx.. ♦
As played i think you should just fold the river.
I'm very interested what this guy had, so please, please tell us! ♦
