how often do I need to update my IDE?
It really depends on what you want from the IDE. If you want a tried and true experience with no unpleasant surprises then find a version that works for you and stay with it until you’re forced to upgrade. If you want to benefit from any new features that have been added recently at the cost of dealing with any bugs and breakage that came with it then always use the latest release. If you want to contribute to the Arduino IDE development by beta testing and reporting bugs and don’t mind a potentially unstable IDE then download the hourly build every couple days.
I fall into the last category and for the most part I don’t mind using the hourly but I also have a bunch of previous releases installed I can fall back on if there is a bad hourly that’s causing me grief.
Is there an easy way to tell what important new features may have been added or bugs deleted? I’m not on the leading edge of anything in the Arduino world but don’t want to miss out on any time saving new bells and whistles either…
There’s a summary of the most important changes in each release in the release notes: Arduino - ReleaseNotes
You can see the current release notes at Arduino/revisions.txt at master · arduino/Arduino · GitHub but if you want the full change log you have to look at the commit history for the Arduino IDE: Commits · arduino/Arduino · GitHub, arduino-builder: Commits · arduino/arduino-builder · GitHub, and any other component that you’re interested in(such as SAM core, SAMD core, etc.).
Now to your specific question of upgrading from 1.6.10. Arduino IDE 1.6.10 has been considered one of the worst releases of all time but actually the major issues were caused by Arduino AVR Boards 1.6.12 which is included with Arduino IDE 1.6.10 but may be installed with any Arduino IDE version since 1.6.3. So you should definitely upgrade to Arduino AVR Boards 1.6.13, unless you want to downgrade to the tried and true Arduino AVR boards 1.6.11. There is only one Arduino IDE 1.6.10 specific issue I know of which was actually an intentional change by the Arduino developer(Limit recursive sketch compilation to the `src` directory by matthijskooijman · Pull Request #148 · arduino/arduino-builder · GitHub) but met so much opposition that they have removed it in Arduino IDE 1.6.11. There is only one new bug I know of in Arduino IDE 1.6.11, which is that it no longer allows some incorrect formatting of 3rd party boards files, which was previously ok. This could cause the IDE to not start if you have one of these files previously installed or if you try to install the file in IDE 1.6.11 it will fail where in a previous version it would have installed and worked fine. I’ve tried to get all the 3rd party files fixed up so this should be less of a problem in the future but I’m sure there are some I missed or the authors may lag on accepting my changes.
Currently Sanguino and Balanduino are the two that have not done so. EDIT: those packages have now been fixed! If you have any 3rd party boards packages installed using Boards Manager then you should do Tools > Board > Boards Manager and wait for all downloads to complete with Arduino IDE 1.6.10 before you install 1.6.11 to make sure the fixed files have been downloaded to your computer.