For the $1000-3000 that a single OA application costs I can pay for a new computer, or send one or two students to conferences, or pay for part of a stipend, finance a temporary web design guy, etc. Now I try to publish 10 papers per year - that's $10-30,000 out of the window for no "return" to our group. For $30,000 I can send everyone to several conferences!
Conferences are more important to a scientific career than an OA paper. The people who hire you will in all likelihood have access to your paper even if it's behind a paywall.
>Paper publications make or break early biomedical research careers.
Yes, but that has nothing to do with the OA-status of those publications - if it's a high-impact journal, then it makes the career, if it's not, then not.
Conferences are more important to a scientific career than an OA paper. The people who hire you will in all likelihood have access to your paper even if it's behind a paywall.