The AF LOVES engineers. Reasoning is because they really really need all you smart folk to keep rolling out all the cool stuff and to keep all the crazy stuff we have running. However, the AF faces a huge problem of engineer attrition because you can make tons more money doing engineering in the civilian world. So, a lot guys do 4 and get out so they can make way more money.
I know a guy who's now doing developmental engineering (he was an aero major); he loves his job. I don't know for sure, but I'd say he was probably in about the middle of his ROTC class. That might be able to give you at least a little perspective.
As far as being selected for engineering, if you say you want to do engineering and you have an engineering degree (assuming decent grades), then you're pretty much a shoe-in. Commander's ranking is decently important for getting exactly what you want, but like I said, you don't need to be in the top 5% to get engineering. I know countless people who have gone into engineering who were the cross-town, nobody knew them, kids. They didn't do a ton in ROTC, but still made it to what they wanted, engineering.
Now, don't take this as me saying you can slack off in ROTC. Do the best you can, volunteer, try to hold good positions, but don't let the people going for rated slots try to tell you that you have to make ROTC 90% of your life to get what you want. Do the best you can in ROTC, but don't feel that you have to bust your ass to be #1. Personally I would bust mine because I like being at the top, but that's just preference, not a requirement in your case.
Sorry, I don't really know of a site like this more tuned to other AFSC's...I know it must be annoying for you with baseops considering it's practically all pilot/nav oriented. Keep looking, maybe you'll find something. Also, a good thing to do would be to find out what guys ahead of you in your position have done. i.e. do you see guys going to engineering who were ROTC studs, or were they just kind of there, did some stuff, and comissioned. There's basically those two ways to go through ROTC. Neither is necessarily better or worse, it just matters on which is best tailored to your situation.
Sorry for the long post, hope something helps out of it. Let me know if you have any questions or would like me to clarify anything I said in this one (as I wouldn't be surprised if I had to ;) ).