I've found that you can block the rocks in with trees then the rest of the ground with paths to stop them coming back, it's a bit annoying to remove them when you want to place something new but cheaper than removing 16000 worth of rocks.
I've been forwarding time but I have to start up where I left off, so my next day will be the 1st of January 2013.
In Ice age you can get Acorns (gem equivalent) in more ways. Daily bonuses (although those have recently stopped giving anything really valuable), Scrat's Kung Fu game (which you get a token to play daily and also works when you forward time. Best way as you can get up to 100 Acorns if you're lucky), Visiting people and finding Scrat. The only one we get in FIM is the daily bonus as far as I can see.