It's hard to call learning japanese as an adult "hobby". The learning curve is step and requires a lot of effort within the first couple of months (provided, you're learning it and making progress); something, most adults aren't capable to pull off due to massive time constraints, work and little spare time on hand. On the other hand, once you pass those first couple of months and learn the basics (kana, basic kanji, vocabulary), it becomes less tedious and more feasible.
Would I recommend learning japanese just to be able to read vn's? No. Would I recommend learning japanese, if you're either a huge japanophile or a fan of japanese popculture? Yes. If you're interested to make another step and move on from translated works to read manga, vn's, play games and watch anime in their native language, you should consider learning japanese. It's because most of the stuff we get translated is usually shit and we often miss on things, that are really worth it. That's when knowing japanese comes in handy.