Jens raised a valid point: that removing the spells and boosting the HD makes the class stronger at lower levels.
What about something along these lines as a remedy?
SECRETS OF THE WILD [Class feature, ranger]
Rangers study the ways of wild animals so well that they can learn a few of their tricks.
Choose one of the following abilities upon reaching fourth level:
• Watchful as the Hawk. A fourth level ranger with 7 ranks of Knowledge (Nature) gains a bonus of +1 to Spot rolls for detecting hidden enemies in a natural setting. At eighth level, with 11 ranks of Knowledge (Nature), the bonus increases to +2; at twelfth level (15 ranks), +3; at sixteenth level (19 ranks), +4; and at 20th level (23 ranks), +5.
• Tenacious as the Wolf. A fourth level ranger with 7 ranks of Knowledge (Nature) gains +1 bonus to Survival rolls for recovering a lost trail (i.e., re-trying a failed tracking attempt). At eighth level, with 11 ranks of Knowledge (Nature), the bonus increases to +2; at twelfth level (15 ranks), +3; at sixteenth level (19 ranks), +4; and at 20th level (23 ranks), +5.
• Stealthy as the Fox. A fourth level ranger with 7 ranks of Knowledge (Nature) gains a +1 bonus to Move Silently checks when moving in a natural setting. At eighth level, with 11 ranks of Knowledge (Nature), the bonus increases to +2; at twelfth level (15 ranks), +3; at sixteenth level (19 ranks), +4; and at 20th level (23 ranks), +5.
Something like this would re-balance the higher levels and also help make up for the weakness of the class after swapping spells for the d10.
I admit that these bonuses are not particularly exciting. I'd be happy to accept suggestions.