That's the statement that makes my heart palpitate and I get an instant headache.
I'm an amateur for the most part, so vacation IS photography.
So are you going to stop taking pictures until the vacation in order to avoid adding any more actuations to the shutter?
You've used roughly 10% of your shutter's rated life, and any concern about the shutter failing should be waaaaaay at the back of your mind. Any of us can tell you what we want about the chances of the shutter dying (slim-to-none, btw), but you are obviously not going to listen (and that's not to be taken condescendingly, it's just an observation from what I've read from you so far).
The advice I'd throw at you (other than not worrying about it) would be to not spend any more money than you have to to make sure you can still take pictures on your vacation if the unthinkable happens and your 50D breaks. This means you just need to pack up your old 300D and have it for piece of mind. That way, you'll be able to go on your vacation, take some photos, and relax!! 



