System Restore only keeps 30-days of restore points. How to increase?

I understand that it is possible via registry tweaks to increase the size of the space allocated to System Restore beyond the 12% limit, but from what I have read it is strongly advied not to do so.

30 days of Restore points should be more than enough - old restore points beyond a month are of little value. System Restore should not be regarded a an alternative to backing up - only System files are backed up.....

System Restore - Wikipedia, the free encyclopedia

If you are really set on having more restore points I suggest you look at incremental disk imaging using Acronis or similar. Acronis can be scheduled to make an incremental backup automatically. Needless to say the image must not reside on the drive/partition on which the OS is installed.