Leveling specs, in my opinion, are pretty flexible... just take what you think would be useful, experiment a little. As enhancement, make sure you pick up dual-wielding and stormstrike at 40. You can level just fine as enhancement or elemental (though enhancement is usually viewed as faster). You can level as restoration too, just... slowly.

At 75 (I think) you get Lava Burst as elemental, which is a fun and powerful spell.

Kind of surprised but your question about wondering if leveling a Shaman that high is "worth it" or "fun". Are you having fun now? Did you have fun at level 1? Enhancement Shamans really come into themselves at level 60 if you ask me, with dual-wielding, maelstrom weapon and spirit wolves. Elemental is great and gets better with lava burst.

60+ enhancement shamans can solo a lot of group quests, as well

Whether it's "worth it" or not.. what do you mean? Can you raid with any spec effectively? Sure. Kind of an odd question.

As for your last question... are you talking about elekk mounts? Well, you can "trade it in" for a different mount whenever you grind out the appropriate rep....