My opinions on your considerations:
1. Going to El Caminito del Rey
Hell yeah, as long as I get to go with you.
2. Getting a cat (yes, I'm still allergic to them)
I love cats and am also allergic, but I have no opinion on this one.
3. Shaving my head
Sure, but do it after #8
4. Getting a tattoo (although not of the cover of the Tao of Pooh)
You know my position on this.
5. Buying an HDTV and a PS3 or Xbox360
No. I don't think you need any more stuff to keep you in your house. As a matter of fact, kill your television.
6. Taking three weeks off to walk around Europe/Australia/Asia/Alaska
Europe - Yes.
Australia - No. Do New Zealand instead. Summit Mt. Cook while you're there.
Asia - Sure.
Alaska - Yes. Summit Denali while you're there.
7. Summiting Everest
Should you start with something a little shorter? (see above)
8. Growing my hair out
Yes. It'll keep your head warm on Denali.
I'll add a couple for you, too:
9. Road trip across the country for 2 weeks.
10. Rim to Rim hike through the Grand Canyon (as long as I get to go with you).