Take it from someone who has tried. Sketchup will make learning Blender harder. The way you end up building models in Sketchup actually is very different from most other programs and once it's ingrained it really becomes a pain in the ass to unlearn it.
As for continuing to use sketchup, your modelling life will be much easier once you start installing some of the many free plugins available. There really is no point to buying the pro version unless you need the timeline tools for working on "projects". (think architecture and construction projects).
Check out this thread
again now that you've played with the program a bit.