I don't know where you are located; but I was once in your position...I really didn't want to become a CFI because of what they made at my academy...
But, at 300 hours, I couldn't get someone to let me borrow a plane even. Try starting your CFI training and then the other instructor ratings. I have only met one person who had their high altitude endorsement with less than 2000 hours, but he had flown Kingairs, so he probably did it out of necessity. I can see how it would look good when you're trying to become a co-pilot though...
Being a CFI is a great experience, the connections you make and people you meet can be of great help in your career. It actually is pretty fun for the first flight of the day, and you can make a decent living for a while. Not to mention that when you apply for jobs, they like that about a pilot; and the regs are engraved in you like you wouldn't believe.
If you're not looking to make this a profession, I would (in your place) get tailwheel, seaplane, and fun add-ons (aerobatics). I think the high altitude could wait until you have some sweet job in your sights.
Good luck.