For comparison purposes, I do think it is easier to keep multiple years of data in my current year’s spreadsheet. I’m wondering if instead of storing all of your transactions from the previous year, you can just keep the totals of each category in your current spreadsheet. That way you can can have a Current Year vs Last Year comparison.
Also, if you are using the Foundation Template, you can try using the Trim Balance History Add-On. This will trim entries from the balance history tab. Check out the link below for more information.