WildWebDeveloper is in a fast development phase. STS 4.8.1 ships 0.10.2 while last stable release is 0.11.3, but it's not possible to update it adding new software source.

With regards to the incompatible POM editor, you can uninstall that feature via "About -> Installation Details", then select that feature from the list and uninstall it. After a restart, you should be able to install the snapshot from WWD again - at least it worked while doing some quick testing here.

With regards to the latest error message, I unfortunately haven't seen that before. Are there any more details (from the More... link? Or a stack trace in the Error Log view maybe?

You could also try to install STS4 from the tar.gz, maybe there is a permission issue with the location you installed STS4 into.