Hi Amadeus, welcome to the forum.
The Template would be accessing the same sounds. So, no, there shouldn't be a difference in what you hear. However, there are not any default instrument definitions
specifically designed to work
exactly with the S7S library patches. Where this makes the most difference is in the unpitched patches. If you're not using any or very much percussion, then you maybe haven't run into any of the common issues people have when trying to write with the S7S unpitched percussion patches.
And on the other side, the Template's pitched instruments are designed/setup to do what I call "no-conflict auto-loading". The idea here is that once you enter one of those instruments into your score, you already know what patch is going to be loaded - especially if you're using multiple libraries at the same time. And if you do need to get into the Mixer, it's most likely to just adjust volume settings.
The templates have more to do with streamlining the workflow than anything else. Since every patch in each supported library has a corresponding instrument defined in its template (custom Ensemble), you can spend more of your time actually writing music instead of messing around with any laborious and otherwise ongoing setup.
Feel free to download the
Readme file, if you have not yet done so. Also,
this overview page may help.
Now, with all that said, if you are satisfied with the results you're already getting, and feel that your workflow could not be improved upon, then there's probably not a need for you to buy the Template.
Please let me know if you have any more questions.
Hugh