As I understand it, the action economy hack of Summon Nature's Ally, by itself, is one of the more imbalancing things about Druids. You can give yourself an ever increasing number of turns. Who needs to tumble when you can run your opponent out of AoOs by giving him a "Bad either way" situation where he can AoO one of a few summoned bears, your bear, your bear mount or you in bear form. Odds are he doesn't have more than the one AoO, and even if he does, you still would have more summoned bears. Just have a bear grapple him and forget about AoOs, anyway.
For how abusive SNA can be, I'm not sure you can remove it without taking away one of the staples of what makes 3.5 druid a druid.
On the other hand, giving them weak combat spells? Yeah, Blasting makes casters overpowered.