One user at a time : In the instance where there are a number of people required to work on a spreadsheet, they can only access it when no-one else is working on it.
Not dynamic : Data ranges become redundant when new records are added, resulting in established formulae needing to be altered. Overlooking these errors can be embarrassing and downright expensive, especially if important decisions are being made based on the data.
You may want to create a workbook with multiple sheets for various aspects of your budget. You can have one sheet that keeps track of savings and investments and another sheet that lists your monthly bills.
Today, there are a large number of options to choose from. The downside to upsizing your spreadsheet to a database system is that databases require fairly in-depth knowledge, especially with regard to extracting data in queries, form construction and reporting.