Here’s some things that might help:

1. Make sure you have the WordPress debug log enabled so you know what files the system looks for in case it cannot find them. You might need to debug the path.

2. You can avoid hooking to the filter altogether, if you use the views_dir argument in your shortcode. This is implemented in 3.2.0 and is discussed in the documentation. It might allow you to do more tests quicker and easier.

3. It could be some issue with the file permissions. Make sure that your files are readable by your webserver and that their directories are scannable (execute permission).

4. You can, but you do not need the directory structure wallets/includes/views. Just call your directory anything, such as wallet_views.