If you price your services accordingly, a few little pain in the ass things are no big deal, and you learn to ignore them.
But, with a contract, it's important to detail what IS important to you. Things like knowing where power is should be detailed before you get to the venue. Power 80 feet away is annoying, but way better than many venues provide.
Building access time definitely is one that needs to be spelled out in the contract. It's best to have that initialed as well, so there is absolutely no question as to what time someone is supposed to be there to let you in. If they are 30 minutes late letting you in, then the show starts 30 minutes late with no fault to you. (now, obviously, you'd likely bust ass a little and try to start as close to on time as possible, but that's just work ethic.)
Personally, I like to have floor plans laid out as well, showing where gear is expected to go, and what sort of space requirements are needed. If I got there and 20 plants were on stage, yeah, that would suck. If there was someone else at the venue, I'd certainly let them know. I'd even be there to lend a hand getting it out of the way if necessary. When you're there by yourself, there's less choice, and you just gotta do what it takes to make the show happen.
Yeah, having extra charges for grossly inaccuracies for the event is acceptable, but sometimes it's just easier to set your pricing based on how hard you're willing to work for any event, and consider the ones that don't have those issues the easy money.
Again, the best way to head these problems off is to make sure communication lines are open BEFORE arriving. The more you have in writing, the easier it is. Giving a simple phone call to clarify a couple days out goes a long way too. Yeah, sometimes people forget stuff without that little reminder.