I think any language is worth learning.

Right now I'm at 5, Dutch (my mother tongue), Polish, German, English and French (the latter poorly through inactivity).

I very much want to learn more languages and I find that with every language added the next one becomes easier.

So there is no such thing as a language 'not worth learning', almost all of the languages spoken on the European continent are related in some way or other anyway (even Hungarian and Finnish).

Whether a language is 'ascending' or 'descending' in influence can certainly guide your priorities but I'd definitely not rule them out simply on that basis.