In one hand, this is easily solvable by making Aim and Build Up trigger the "in combat" flag.
On the other, if you use Aim+BU with a slow snipe it really should hit like a truck. While the Aim text says it "slightly" increases damage, it actually increases damage by +62.5%, which is definitely not "slightly".
Question is, do you ever use the slow snipe? If not, try the Fast Snipe proc in there and see how that "feels". And remember that Aim is not just ToHit.
Okay, did some more testing, jumping back and forth between beta and live with my lvl 32 electric/martial blaster. Compare and contrast. He has a few partial IO sets on live, but just SOs on beta.
I mostly solo with him. Here's how I typically run him. If there's a single bad guy, I'll pop any reds I have, hit Aim, and snipe him. If there's a couple of bad guys, say, guarding a prisoner, I'll usually snipe one, then blast the other one or move into melee range, often with Voltaic Sentinel assisting.
If there's a group, I'll hit Aim, then port into their midst with Burst of Speed, followed by Dragon's Tail, Spring Attack if it's up, then Ball Lightning, and if necessary, Short Circuit. If somebody survives all that, I might hit him with an insta-snipe if it's available, or hit him with Storm Kick and Ki Push -- and if he survives that, while he's drifting gracefully away, I've got plenty of time for a non-instant snipe. I've got a pretty good rhythm going with that, provided I don't miss-click something. Burst of Speed seems a little finicky at times.
On live, I played a defeat all vs Freakshow -- smooth sailing. In one room with a lot of guys wandering around, I used snipe (with Aim and without) several times, and if the target didn't die, following up with Lightning Bolt would do the trick. Most of the rest of the time it was the combo platter described above.
On beta, I played a rescue mission vs Crey. I tried to play just as I would on live, but something felt off. Seemed like the insta-snipe was often there when I didn't need it, but if I used it, it wouldn't be there when I did need it. A few times I found myself ready to use it, like when a target was drifting away after a Ki Push, but had to wait for it. I think I'd adjust eventually if I played it like this for a while, but again it seems perfectly fine to me on live just as it is right now. This is from a blaster point of view, of course. I've got a fire/martial dom in the low 20s, but no snipe there, so I don't know what issues dominators may be having with it.
D'oh! -- I forgot to try that Fast Snipe IO.