A major upgrade offers the chance to do some spring cleaning, eliminating unused items and streamlining the user interface. Moreover, Microsoft may have anticipated some of the features you have been seeking and included them in the product.
Here is a good place to start in reviewing what is new: http://www.microsoft.com/en-us/dynamics/crm-customer-center/what-s-new.aspx
Dynamics CRM 2013 and 2015 include a major overhaul of the user interface compared to the 2011 version, so you will need to prepare your users for a bit of future shock. The good news is that you gain instant multi-browser and mobile device support.
You will save time and money because both the upgrade and the new enhancement require testing, so why not do both and the same time and test once?
If moving to the Microsoft CRM Online cloud is in your plans, the upgrade is an opportunity to take the leap. Once your organization is on Dynamics CRM Online, you will automatically be required to stay current with upgrades anyway.
Be sure to upgrade all the way to the latest current version, Dynamics CRM 2015, rather than stopping with 2013. The old practice of waiting for a few minor versions doesn't hold up very well.