What's a smart way to use/maintain two separate bash_profile's and vimrc's

Use an environment variable. This way, you can set THEME=dark or THEME=light in a shell, and all programs started by that shell will use the desired scheme.

In bash or any other shell:

case $THEME in
  light)
    PS1='\[\e05m\]fancy stuff\[\e0m\]';;
  *)
    PS1='\w\$ ';;
esac

In your .vimrc:

if $THEME == "light"
  …
else
  …
endif

You can use soft links. So create two sets of .bash_profile and .vimrc with the contents

touch .vimrc-light .vimrc-dark .bash_profile-light .bash_profile-dark

Then depending on your mood, change the softlinks to point to the right colorset

ln -sf .vimrc-light .vimrc 
ln -sf .bash_profile-light .bash_profile

I'm developing a tool, shprofile, that helps you to manage a set of shell profiles. Each profile defines a set of scripts that can be loaded at any time within the current shell session.

To solve your issue, you can then define 2 profiles that contain your 2 versions of .profile and .vimrc. Then you can switch between them by calling shprofile:

$ shprofile profileName

For more information, check out the associated Github project.