Why would you want to level as destro?
Check out this comment on leveling. I would suggest looking at the demo or aff trees for leveling purposes.
In regards to the trinkets, spellpower will always benefit you more than haste, except perhaps in some extreme gearing/encounter scenarios that you won't be contending with as you level. So yes, while probably the absolute best situation is to get 2
Discerning Eye of the Beast trinkets, I don't think it is that much of a make-or-break decision on which to use as you level your lock. After all, the general lack of trinkets altogether means most characters at lower levels have no trinkets or (usually) inferior ones from quest rewards. Based on the equip effect of each after you kill mobs, it might be useful to have one of each, thus you restore both health and mana from each kill and get both a spellpower and haste benefit. You'll kill mobs quicker and be able to utilize Life Tap better.