In regards to question 1, my opinion would be yes, collectors and battlers should still put forth effort if they desire all their pets to be max level. LeCraft Tweeted the bit about the "leveling stones" but provided no additional detail.
We really don't know what leveling stones will entail. Possibilities include but are not limited to:
- They provide only a portion of a level and not the full 25 levels? Or full 25?
- Limit use of one per pet? Other usage cooldown?
- Extremely difficult/rare to find?
- Other limiting factors?
It's even possible that it's an idea they liked in the beginning but then end up scrapping later as work on WoD progresses. So until we know for sure what the stones will be all about and the details behind it, I wouldn't drop your leveling efforts. You might regret stopping now in hopes that leveling stones will be a quicker method of leveling up, only to find that they're not what you thought they would be. Maybe once more information comes out, it'll be something to consider.
Just my two cents.