I ride English but find riding western for pleasure is very fun and the saddles are slightly more comfortable than English. I'm not interested in taking western lessons, but I think it would be fun to get a western saddle just for fun. I've hacked western before, but again I don't want to take lessons. Should I get a western saddle just for fun? I know my horse has been ridden in a western saddle before.
Personally, I ride my mare in her Aussie/stock saddle almost exclusively but I also have a western saddle that's my size and a child sized western saddle for her. I teach lessons on her to a few kinds so the kid-sized western saddle comes in handy pretty often.
I don't use the "me-sized" western saddle all that often but sometimes it's just nice to change up the pace. :)
I'm in agreement with everyone else. If you enjoy riding in a western saddle when you're out riding trails or even if you someday did want to enter a novice western class at some local show, then having a western saddle is always a good thing. Heck, I am a devout western rider and I owned an english saddle for a time when I was younger.
Definitely worth it if you can afford another saddle. Like others have said, you can find really nice used western saddles if you look in the right place. If you trail ride a good amount it is nice to have a western saddle for the added comfort and extra security. I am a western rider and will occasionally ride english for fun. But I don't actually have my own english saddle because I know then I will be stuck riding with it on our trails. Not a bad thing, but with my gelding it surely doesn't extend my life expectancy. XD