interesting discussion. I'm like you, only have shot a few budget ones for close friends here in australia. They hire their own pros back in the home countries so didnt want a full one here again for their engagement ceremonies.
Few things to note.
Whether you are paid high or low amounts, if you are paid then you will need to man up and work like a pro. there are many strategies to this some subtle, some more in your face kind of styles, taylored to suit which ever kind of "uncle bobs" who stand in your path.
First I think you must practice to exude confidence in your work. As you have said, the BnG are impressed in your work that is why the hired you. Plus they have compliments on your shots at the end of the day. Hope that boosted your confidence.
When the couple hire you, the first thing you should do is start up a contract. Take a look at how some of the pros word theirs. This is to protect you in the event that you are blocked out and cannot get the shot, then you will still be paid. During this contract setup, make sure you discuss some of your ideas and also bring in the event you might need their help to take down uncle bobs as a last resort. This process is very very impt. You MUST make good rapport with your client!
You will definitely need to take charge during the event.
Try the "befriend" attitude. You will need to build up rapport with everyone on spot esp right at the start eg in the morning during the make up and dress session. These are the first line of attackers from their side. If you can get them on your side, the rest of the day, it will be easier.
Means you will have to put in the effort to arrive earlier probably. To have time to talk to them. discuss a bit of your ideas for the day, try and make them cooperate with you.
Once you can do that, they may even help you out for the rest of the day to take down other Uncle bobs

Of course get on the wrong foot of theirs and all hell breaks loose.
If you decide to go out all guns blazing like rambo, and use the 300 f2 to whack, dont whack their head. Whack their more expensive cameras

"Opps sorry ah, looks like my cheaper lens is more robust than your gear" kind of attitude. Dont be sorry, cos they were in your way. :devil:
Another strategy is to get the BnG to help you. Their power on the day is the biggest. That is where the contract terms comes in. Plus your previous discussions with them. This weapon must be used discreetly for max effect as previous comments pointed out no one want to be embarrassed. other than the uncle bob who needs to be.
Eg pull the bride to the side discreetly and show her one or 2 "not so essential" photos and say "oh this photo would have been so fantastic if not for so and so". Unleash the bridzilla in her on the said so and so. If effective, sit back and watch some fireworks.
End of the day, there might be someone who is really difficult to deal with.
I have heard on flickr forums where uncle bob is so powderful that they can even utilize the pro's lighting system to their advantage!
eg you have pocketwizard trigger? they bring their own and switch to your channel and use...
or even worse disrupt your flow by popping it off from somewhere else :bsmilie:
All the best with your passion!