Is there a plus to linking to relevant sites? Or is there only a downside to linking to sites? (Basically wondering if I should attempt to try to link to other places like my community)
Linking to relevant sites gives you the benefit of having your site listed in as many relevant locations as possible and also gives you direct traffic. so yah, i say it's a plus.
Linking to other sites lends some credability to what you are saying. Plus, when the other site gets traffic from you, they might notice you, and send some back.
Google wants people to visit good resources. A site that links to a lot of good resources is regarded as a trusted site.
The amount of clicks on the link would be lower, you won't get much targetted traffic to your site. Also a relevant link would more strongly influence ranking potential of your site as compared to a non-relevant link.
Using common sense is always good. Linking to a relevant site would make sense if your site is actually about the topic you are optimizing for. Right? If I have a site about Poodles it would make sense that in addition to having lots of information, pictures, or other related content about poodles on my site, that I would also link to other great resources (aka websites / web pages) on the same subject. Are you going to rank #1 on Google because you link to the Wikipedia poodle page? Not likely, but it will most likely help.
Alright - would you say this the same for forums? Because if I like to "relevant" sites it would most likely be similar communities like mine, no?