I'm not a member, but have competed in CTR. I say go ahead and do the competition, even if you don't do well you'll have a score that breaks down and shows you what the problems are and where you need to problem-solve. If you do pass/fail you don't get as much detail or a score so you won't be learning nearly as much.
Here are some important things to think of:
1. Don't let your horse eat or move during P&Rs...their pulse will go up (it's ok to let them eat--just not DURING the P&R--but before the vet check it's good because it'll help their gut sounds)
2. Make sure you take the time to let your horse drink...and to sponge water onto them if they won't drink(before P&Rs you should make sure they are drinking and sponge them all over to cool them down as much as you can. Also, if they aren't great about drinking I'd consider electrolytes.
3. I'd wear a stop watch as well as something like a GPS that can measure how far you've gone. This way you can make sure you know how much time you've got left, how much distance you've got left, and what pace you need to keep. This is huge. You want to do the first half faster than the second to allow for unexpected incidents and so that you can walk into the hold/finish instead of rushing in. :)
4. Before competition day make sure your horse is used to having your hands all over him, a stethoscope all over him, his lips pulled up to look at his teeth, etc. You don't want him jumping all over and giving the vet a hissy fit. If he kicks/bites the vet can take a behavior penalty...if he flinches too much he/she may think there is pain going on...pulse may go up if your horse isn't used to the stethoscope, etc.
Hope that was helpful...it's all I can think of at the moment!
I LOVE competitive trail! I've done other stuff --Jumpers, Hunter-- thinking that I wanted to make it big and be glorious. Then I figure out that all I really wanted to do was party and gallop around bareback with like minded people!
Most people aren't in for the prizes, just for the fun. We love being around other horse people, helping each other, and enjoying ourselves! It's a big party. You usually will even forget it's competitive, because the ride is so casual.
The biggest tips I can give you are condition your horse well, keep the pair of you well hydrated, and watch for those orange flags. I can't tell you how many times I've gotten lost...
Also, poke and prod and mess with your horse all you can. Practice going through the vet checks and everything. Make sure he stands quietly and is polite. Manners are a must! It'll be easier on you both.