Great guide! Especially as after patch 1.2 comes out the engineer will become even more important.
Just a couple of tips that i think are appropriate.
1) If commander assets are destroyed, it's safer to jump into an APC and park next to the asset. That way, you're repairing the asset, AND looking for that sneaky Spec Ops. Chances are he'll have used up all the c4 anyway - but be alert. Obviously, a prone engineer repairing (thus staring straight at) the UAV or Arty is a perfect target for any hidden enemies.
2) One of my favourite 'teamwork' rounds was playing in squad of engineers - we all hopped in an APC, drove around shooting people, as soon as we were hit, the driver would pop the smoke, and two of us would get out and repair - took 3-4 seconds, enemies usually dead, we get repair points. Easy.
3) If you're in a chopper as an engineer - NEVER try and repair ground vehicles by hovering above them close to enemy lines. A chopper attracts fire like playgrounds attract pedos.
4) If you're commanding, the best class to be is engineer - chances are that your squads won't give a crap about your assets, and even after you've ordered them to repair, they'll press page down and demand a UAV. So, repair your own assets if no squad complies, after all you get repair points for them (THIS IS A FACT).
5) I find the Jackhammer to be useless. As you said, inaccurate, long reloading times etc. However, the USMC pump is a killer weapon - and i like the MP7 too. Don't diss this unlock, it's deadly provided that you're dealing with 1 enemy. With its uber-fast rate of fire and 20 rounds, it's very good. Also 1.2 will make it even better, with possibly 40 rounds and a slightly slower r.o.f. So all in all, i choose the USMC shotty, if PLA or MEc i take the MP7.
6) Engineers often forget to zoom in when fighting in close quarters. I can't remember how many times people see i'm an engineer and probably think 'haha easy target'. So they just take their time, lie prone on the ground and fire at me. Mmmm. A quick jump + prone (this isn't dolphin diving, it can be done in real life), zoom in on the shotty, one blast to the face and voila - enemy wasted.
7) A cool way to get repair points - and i hope chuy doesnt consider this to be 'expoiting' is the following: get a humvee, drive to wherever the enemy is and hop into the back. GLs will start coming your way, you'll be safe in the back repairing and getting closer to your elusive 25 repair points. I don't think it's exploiting!
That's about it guys, i love playing as engi but now i have my experts i've turned to sniper.