Yeah, I would stay away from elixir infused bombs in the healing build and swap the bomb kit for tool kit. The defence you get from the gear shield can be invaluable during large group fights, and the pull can be useful in quite a number of ways. Plus, it can be rather unreliable to heal people with bombs in large scale combat because people will generally be moving around a lot, and any healing bursts are facilitated by eles or guardians.
It also might be useful to take on the shield instead since it gives you a blast finisher to use in your healing turret, although that would obviously result in lower damage overall.
I have a condi-based healing build I use for similar purposes: http://gw2skills.net/editor/?fdEQJAqelUUpvrlcxdLseRSdBNqoE6QMiBCqAIyEuQA-TxRDABH/gA0S5HU7PsieCdU/BgTIggKBJFgTrBA-e
Back in the day, the case was that incendiary powder fit nicely into this build, so it was a burning/healing hybrid with dual pistols, and it actually had somewhat decent damage. After that trait was moved to the master tier, however, the build was crippled beyond repair, so I ended up converting it into this high healing power thing.
The damage is quite low, but it is pretty effective at healing itself and others. As I mentioned, the nice thing about using the shield is the quick access to a blast finisher, as well as being able to keep rangers off your butt quite well. But a power spec with the rifle will definitely bring more assets as far as offence is concerned.
One tip I will mention in case you aren’t doing this: I find trying to combo your F1 with rocket boots to be a fairly efficient use of the ability. I see a lot of people just popping the F1 to tickle themselves with a bit of regen, and they completely miss out on the extra blast finisher they could get. So if you get snagged and need to use your boots, I’d suggest getting in the habit of using your F1 and then boots immediately after. This causes only a short delay, and gives you a healing burst that you would otherwise miss out on. Since the two have similar cooldowns (especially if you invest points in the tools line), you can pretty much guarantee to have your F1 ready when your boots are off cooldown, so I feel it’s just a good habit to get used to comboing F1 with your boots.
As far as things with sinister go… You could possibly use a PvP build, but modify it to use sinister instead of celestial (i.e. http://gw2skills.net/editor/?fdAQFAUlUUpErlcxdLseNCbBNqxI6NWlO+5DEgkC-TJRHwAFeAAc2fAwFA4YZAA but with sinister gear). If you didn’t want to use grenades, you could always take 2 points out of explosives, dump them in firearms for hair trigger or in inventions for cloaking device/protective shield, and then swap shrapnel for empowering adrenaline (I usually use empowering adrenaline anyways). The problem I have with sinister is that a condition engineer is just not that dependent on precision, particularly since things like grenades will hit multiple times and fury is fairly accessible. You still want some precision, but I don’t think it’s worth stocking up on a lot of precision in exchange for vitality or toughness. So you might try using only part sinister (i.e. sinister trinkets, but then maybe celestial/carrion/rabid/dire for the other stuff).
Perhaps a roaming build that utilizes Elixir Gun and Tool Kit? I also like EG a lot and can’t imagine a build without it.