I double-degreed (BA & BS like the OP is talking about--that's different than a double major some other posters refer to). I had a minor too. Programs weren't that interested in the fact I was a double degree (and non cared about the minor). They were more interested in the fact one of those degrees was in art--it gave an interesting topic to discuss.
I bothered for the second degree because I really love art and the only way to register for art classes as an underclassman was to be a major, since then you got to pre-register for them. So I was a double-major and that let me taking an art course every quarter, including over the summer. Then I realized I was on track to meet the minimum number of units for the second degree (I think we needed 20 or 40 additional units in addition to the minimum for a single degree to get the second degree)
If you think there's a possibility you may want to use that psychology degree in case you don't get into medical school, that's where having that second degree would come in handy. Though I'm not sure what a bachelors in psych will actually let you do--serve pizza? Everyone I know that majored in psych and wanted to go into the field went on for a master's or PhD/PsyD.
If you're stuck there for an additional semester anyway, I think it really comes down to what would would you want to do with that extra time? If you want to take those psych classes anyway, you may as well get the second degree. But, think about what courses you'd like to take before you graduate--whether for fun (acting, music, p-chem...) or because you want to learn more (additional upper-division bio, etc.)
Or just take only calc and pay part-time tuition.