I do a fair amount of riding like that and I don't notice much difference in how others treat me. Like you said, "if you are confident and look like you know what you are doing...", that's the key. On the other hand, drivers that don't like roadies because of groups taking the road, running signs, etc. may be more likely to get upset at some "lance wannabe in full kit". Personally, I think it all balances out, which is why I added generally.
I've been riding for 5 years (approx 6k-7k miles per year) and have had only 2 negative experiences compared to 4-5 positive experiences with drivers when training alone. I've thought about why this might be for awhile and here is how I break it down:
70% - I live/ride in an small suburban city with wide roads, bike lanes, and little traffic.
15% - Ride with confidence & speed. Look like an athlete (if possible. This is NOT something you can fake with a pro-kit).
10% - Respect the law & ride like you are a car. Wave thanks at drivers who give you the right of way. (I will run lights/stops when it's early and there is no traffic).
5% - Team sponsor. Our team is sponsored by 2 companies well known/respected in the area & both are construction related. I think the name recognition helps us get respect.