In my opinion, I don't see why you'd spend time learning Catalan. It's not a common language at all, and isn't mutually intelligible with spanish. It would be doing the work of learning a completely new language, without making any distance from Spanish. By that I mean, say you learn spanish, you learn a very distinct part of the world's languages, then you could:
1. Learn Catalan, and not make any step into another style/branch of language, yet put in a lot of language learning work. +like a small country or something
2. Learn something like Russian, and have a completely different branch of language, a different worldview. +like all of eastern europe
If learning many languages, it's good to diversify, I feel, since you will then get an insight into completely different cultures, and linguistic beauty. But I suppose if you aren't fascinated by the individual beauty of the world's different languages, then that doesn't matter much. Just think, Russian is hard, it's different, but it's even still, the same writing system as English and Spanish. Different orthography (naturally), different sound system (by far, but that's common in even similar languages, look at Swedish and Norwegian- mutually intelligible, yet sound very different), but it's still a letter based system. If you learned Chinese, you'd be learning a VERY different... Everything.
Diversify your portfolio. Neither Spanish nor Catalan will help with Russian, learning another language before Russian (you've done already) is good, since Russian is on a bit of another level in terms of grammatical structures and whatnot. I couldn't imagine going into Russian without already knowing about conjugation and parts of speech, since those are just the beginning with Russian.

Geographically, I cant imagine there's anywhere where you couldn't just speak spanish to someone, and had to speak Catalan. C2 in Russian takes multiple years. At least 5, depending on if you spend 2 dedicated hours a day, or 30 nonchalant minutes a day. Text en catal Heres a page in Catalan. I can read a sentence here and there with year 2 Spanish, but it seems like it's orthographically very different to spanish. I cant think of how Russian would help at all for Catalan.