Thanks for the link Bitt. Unfortunately, none of the listed programs is an alternative, but it did help me find at least one other program I can use along side Sketchup.

Live Interior 3D from BeLight is a nice little app I had seen a couple of years ago. It's matured quite a bit since then and seems to be the perfect tool for working on building interiors. A lot more streamlined than Sketchup for this task since it's the program's specialty. That allows me to use Sketchup to work on individual objects, including potentially some exterior scenes, rather than complex interiors or other scenes requiring multiple complex objects.

Most of the apps listed, including the number one "alternative" were more traditional 3D modeling apps for creating poly-based characters and organic objects. The biggest advantage Sketchup has over everything else is that it's a sort of hybrid 3D CAD and illustration tool with a foundation in real-world metrics and scale. It just needs tweaks to make the creation of certain shapes easier and more intuitive. And of course the tweak I mentioned to help navigate the UI and objects.