IMHO, there are several options:
• Make the buttons smaller. Don't scale them, though - they're designed to work at a certain dpi, and look terrible if scaled up/down.
• 'More' button. AFAIK, already implemented.
• Consolidate similar tools into one button, similar to what Adobe products do. Click & hold to select the proper tool.
• Allow an optional double-rowed/columned setup for lower resolutions.