It's not like it's a balancing act between the two, though. Spending more effort on presentation doesn't necessarily mean that the functionality will suffer for

It's not like it's a balancing act between the two, though. Spending more effort on presentation doesn't necessarily mean that the functionality will suffer for it. People that are more aesthetically inclined can contribute better presentation for the software. Since it's open source, those people could be anybody, not necessarily software developers. That someone might want to design logos seems like a pretty different desire than making functioning software, so it's not like you would be diverting effort away from the actual software. (OSS programmers could also want to design logos, but that desire doesn't seem like something that would contradict their desire towards contributing to OSS.) If you want more design-inclined people to contribute you'd have to market towards those kinds of people. So it seems like a catch-22.