My recommendation is not to learn a new programming language, nor any particular database management skills, unless you plan to become a serious developer.
Rather, my recommendation would be to learn the various aspects of PageLines Framework and the creative, innovative ways to use the system to your advantage.
For example, if you read through many of my replies (and those of my colleagues), you'll see that using the Framework to solve what seem like complex topics can actually achieve spectacular results, either with or even without any custom coding. While it may seem complex, one can manage sidebars with incredible dexterity using a combination of Drag & Drop, Page Options, Site Options (Layout Editor) and PageLines Meta Settings at the page level, letting you display sidebar content in different ways throughout your site. Most people don't know that and ignore reading the documentation.
Another great thing to learn is proper image management, using WordPress and any good image editor. Many people try to let WordPress scale or resize images, but don't understand the difference between scaling and cropping, resizing and aspect ratio. All too often, they ignore the memory requirements of huge images, and try to load 10 or more of them into sliders, only to discover their page is slow to load, or that IE displays the full-size image.